Okay, this is actually kind of fun.
It was a counterexample to show that the ability to manufacture and the ability to maintain and repair are not necessarily linked (correlated, yes, linked, no).
Okay, cool. Not a good example (Denmark connected by trucks and jets to the world's manufacturing centers is NOT Regina separated by parsecs from the industries of Rhylanor), but I do agree with the underlying argument - if TL-7 WalMart can manage it's Just-in-Time inventory system, Regina can certainly figure out how to keep enough parts on hand to meet routine demands - with the caveat that sometimes things don't go quite to plan, and the guy in the TL 15 Free Trader may still find himself stuck at Regina waiting months for that uniquely TL-15 part for his fusion plant. But, that's more the exception than the rule. (I wish it was a bit more the exception in the modern day, but that's another story.)
I wonder if they'd give him a loaner.
It's [TL 15 worlds dominating the market]
something I think the canonical setting description disagrees with. (And hence I do too).
As do I. The tricky part is coming up with a good rational to support the canonical setting description.
Page 89 of MT:Imperial Encyclopedia states that maintenance can be performed at a Class A or B starport. That's without any qualifications, so that would be any class A or B starport regardless of the tech level of the system.
Agreed. Routine maintenance up to and including that annual maintenance bit can be conducted at ANY Class A/B starport. On the other hand, "In any situation, repairs to a damaged ship following a battle must be conducted at shipyards of the required Tech Level (although it is an option of the referee to make exceptions to this rule)." (MT Referee Manual, Pg. 96) That's pretty clearly restricted to battle damage. One could argue for not applying it to civilian craft; there are a lot more Free Traders out there than Imperial cruisers, and the port's more likely to have the needed parts in stock. But, that's an IMTU decision, not explicitly stated in canon (though they very kindly gave us permission to do so

).
...The unstated fact is that the rules are simplified for the sake of running role-playing campaigns, quite possibly to the point of being wildly misleading if any attempts are made to deduce setting ramifications from them.
I suspect that the rules and the setting were written... how shall I put it... with a considerable degree of autonomy from each other. Obviously there are setting ramifications to be mined from rules and rules to be derived from settings. And no doubt some of that did take place, at least in broad terms. But I sincerely doubt that the rules writers spent a lot of time working out detailed ramifications of the setting and vice versa. Not even when they were the same people. ...
And, again, I agree with you. That doesn't solve the problem. What rationale can
we apply to resolve the conflict they created for us? Or, do we alter rules to preserve setting? Or, do we alter setting to preserve rules? Or both? Any of those are acceptable solutions within a given person's private universe, but my preference would be to preserve rules AND setting, without just shrugging and saying, "Well, that's just the way it is."
Let me try to put it another way. You seem to be arguing[*] that if the rules are a comprehensive and accurate reflection of the game reality, the setting would not include many TL9-14 ships because they would be outcompeted by cheaper TL 15 variants. Whereas I'm saying that since the setting (seemingly) does include shipyards building TL9-14 ships all the time, the rules can not be a comprehensive and accurate reflection of the game reality.
...
And, I would be right. And, you would be right. Ergo, rules and setting are in conflict - which you seem to agree with.
Ever have a splinter you couldn't get at? Inconsequential, the thing isn't going to kill you - it doesn't even really hurt that much - but it's devilishly hard to ignore. This is one of those things.
And, honestly, it goes a wee bit beyond that. Following rules, I'd be putting players in a TL-10 Free Trader that, even if they filled every room and crammed every inch of cargo space with cargo, couldn't make its monthly payments. Sure, they could speculate; if they didn't lose the ship before they got the hang of it, they'd do OK, but that's a pretty big 'if'. Or, I could bend rules and declare the ship to be the same price as the old CT ship, or put them in that nifty TL 15 model - all of which just gives me that niggling "splinter-in-your-finger" feeling.
If I'm watching a medieval movie and - through some collosal blunder on the part of the director - a peasant shows up with a Timex on his wrist, it spoils the movie for me. I remember watching Star Wars for the first time and hearing Harrison Ford prattle on about making the Kessel run in less than 12 parsecs, and I about had a kinipshin. For all the occasional bits of nonsensical magic-tech (sandcasters vs. lasers, etc.), I do not come to Traveller to play Flash Gordon; this is one of those obscure little details that just bugs the heck out of me.