Professional proofreading is not essential; in fact, in technical writing of various specialty fields, it often results in introducing errors unless the proofreader is trained in said field.
However, the level of writing quality and layout checking across the industry is BETTER than what Mongoose has been willing to deliver. Given their rapid schedule, it is also obvious that very little playtesting can have been done, if any. There is also little evidence, and insufficient time in their schedules, to ahve playtested the supplements well, if at all.
Aside from the list of accredited playtesters in each book, you mean? All game companies, from the biggest to the smallest have errata in their book releases. The better companies produce errata documents after their releases, as Mongoose does. There is no real evidence, beyond your own assertions and anecdotes to suggest that Mongoose is any different in standards.
And to bring it back to the Pocket book again, it again needs to be restated what the criticisms were: that one sidebar table got nerfed by mistake, and one of the deckplans has gone wonky. All the deckplans are already available as free pdfs, and indeed on the practicable level you would need to download them to use them anyway. The missing table is more of an issue, although it is quite easy to remember a ratio of accumulating a level of 1 ton of fuel per week, per level of Power Plant rating.
But lets put this into context:
- The D&D 4th edition Player's Handbook, released this year, had 11 pages of errata in it to correct from it's initial print run;
- The Star Wars Saga edition had an entire print run with several blanked out pages in it;
- SJGames' GURPS actually has an errata mailing list you can join.
- Ars Magica 4th edition forgot to include a difficulty table for it's core mechanic and left it like this for about 8 years;
- Wraith the Oblivion forgot to include any concrete rules for Willpower, Pathos and Passions in
both editions of the game;
- The Great Pendragon Campaign didn't include an index;
- Serenity RPG didn't include an index
or a character sheet;
- Call of Cthulhu's Beyond the Mountains of Madness had a contents page that had every chapter listed with identical page numbers;
- Castles and Crusades frequently gets pillared by fans for it's 'standards';
- Classic games like Call of Cthulhu, Vampire: the Masquerade and Feng Shui are littered with errata, as have been loads of Traveller releases in the past too.
- Loads of 'Indie' games have terrible writing habits and poor grammar.
Sure, there is a couple of mistakes in the Pocket book, and some of the other Mongoose releases, but you are being one-eyed in your criticisms by suggesting that Mongoose are on a different level to any other gaming company.