That's not a problem with Beta-testing, but a problem created by conventional publishing houses.
Publishers are usually publicly listed companies, they rely on shareholders, so when they sign up a new game, a deadline for it's release is established, and the developers will be punished by steep late-fees if they don't release on the deadline (the shareholders need to be kept happy, and see a return on their investment within the promised dealine, they are buisnessmen, not gamers, to them it's just a product like any other).
Most developers, even the really big ones, cannot afford to pay thouse late-fees (they are HUUUEG!), or atleast can't afford to pay them for long, and the established dealines tend to be too optimistic, so this is why we see so many bugridden releases that require day-1 pathes.
So it's not because the Beta-testers are failing at their job, chances are, they just wheren't given enough time to find and fix the problems before the deadline ran out.
Hell, sometimes i suspect there wasen't even time to Beta-test the games at all, and they just had to be dumped on the market as-is before any bug-squashing could take place (especially the PC versions, as thouse are usually the last thing that gets made in a multiplatform release thease days, and thus the most likely to not have been tested and fixed before release).
Thankfully, TWI are not publically listed, and thanks to Steam, they have not had to deal with the conventional publishing houses either, they are independant, so nobody is going to hold a gun to their head and force them to release the game before it's ready, nobody will demand late-fees from them (this is why Steam is a good thing people, even if it's not perfect, and has it's fair share of pitfalls, it beats the hell out of conventional publishing houses if the developer can stay independant).