Actually, in the UK we didn't find out much of what was included in the game untill a couple weeks from its release, even then it was sketchy. As far as I knew from then on the sounds 'may or may' not be included, as launch grew closer this changed to 'unlikely to be included' and then 'will it be included it the big day 1 update'. I heard or saw of no solid answers from PD, something which has been talked of elsewhere on this site. In short, no one knew what was included untill we got it. I believe that's why there was so many pre-order gifts, to get people to buy even though there was little info on what the game had improved on.
Come on, think about it. It's impossible to get recordings for all of those cars. Some of the cars are in museums and haven't been driven or run for years. Certainly, the rarities won't have been recorded. Owners (private, manufacturers or museum) wont be handing over cars worth millions to a games development company to put said car on a dyno and risk it blowing up in the process.
Take the Bentley Speed 8, the model in the game was raced only once, at Le Mans in 2003 which it one. Of the other Speed 8's, only one was sold to a collector in Japan (chassis 2/3) on the proviso it will never be used in competition again. That car is now owned and kept by an American in America. Chassis 4 & 5 have never been run because of damage or display purposes. Bentley own chassis 1/3 & 3/3 and consider them priceless and do NOT allow them to be thrashed, either on track or dyno. When they are driven for PR duties they are heavily restricted (arround the 400hp mark, if that) with strict rev limiting. Bentley's engineers are all over the car like the plague during the excersise. With the massive detune and rev limiting, it's impossible to get the real sound from the car.
The Corvette Stingray Concept Car (one in existance) is still owned by Chevrolet, doesn't even have it's original engine (having gone through different blocks during it's time) and has even tighter security than the Speed 8. Also would you allow your 250 GTO to be dyno'd? I wouldn't, the last one bought that I know of was by UK tv presenter Chris Evans. I believe it cost him £12 million GBP. At that price, you just wouldn't.
The only people saying the sounds would be patched in the day one update were members of the public on fora like this one. I never expected it myself, because I never thought this new synthesis would ever make it to the PS3 in the first place - glad to have been wrong about that. Kaz did say it wasn't going to be in the game at launch, though. If people bought it expecting differently, then the thing they should learn is maybe to research a bit first:
caveat emptor and all that. Not that PD did anything expressly wrong, in my opinion.
Regarding recordings, it just depends on what you want. With a ground-up system, it'd still be very useful to have "proper" recordings, but you only need a few characteristic recordings and the clever boffin stuff takes over. You could even, theoretically, get very close without ever turning the engine over - but I can't see such effort being necessary for many cars.
Besides, if a car can't handle a dyno pull or two, in a properly equipped garage, then it can't handle being driven properly either. That may genuinely apply to a few cars in real life, but all the more reason to make digital copies of them. For cars that no longer exist, you can still make a lot of guesses and get it to sound convincing with no recorded material at all - for instance the VGT cars will have wholly fictional sounds, most likely, as that's how manufacturers start for any car these days (using proper simulations in many cases).
There are always substitutes, too. Honda was intelligent enough to build replicas of its '60s GP cars, these get a good thrashing every year, as they should. The Bentley Speed 8 used a modified R8 engine, so an R8 would probably cover it for most of us plebeians - practically any turbo flat plane V8 at a push. Any Chevy V8 (with the same firing order) could be made to sound like the Stingray racer, it's just getting the finishing touches right, such as the specific exhaust construction for the final colouration - frankly, that's Chevy's responsibility if they want their car to sound right, otherwise they will have to make do with some other facsimile.
Since they haven't been shy about using substitutes (however in appropriate) in the past, I expect that's what PD will do in the future, too.