The way I see it this problem comes from the fact that GT5 is a weird Game/Sim hybrid and as such attracts both gamers and 'sim-players' (for lack of better words).
Usually a sim is all (and only) about the simulation aspect. You grab a car/plane/boat, choose a track/country/body of water and drive/fly/boat around. I haven't played many real sims, but the ones that I have played never had locked content (unless it was in the form of extra licenses for which you had to pay real money).
GTR evolution is a good example of a racing sim. You can pick any car you want and drive it in either a simulated season or your own events. No money, no unlocking involved. Just driving
On the other hand you have ofcourse the 'arcade games' like the amazing Burnout and MCLA. Hardly any simulation of real world physics, although MCLA has some licenses to real cars (so they look the part).
In GT5, the game part is flawed, there is no denying that. This makes the game part very tedious and for those of us who like to play sims, this is a big brick wall standing in between the user and his fun. GT4 had a more logical (and more realistic) progression system and as such that game had less people complaining.
So, as I said before, sim-enthusiast don't care that much for the gaming aspect and if/when it stands in the way of enjoying GT5, I can imagine people asking for a time savers pack. By removing the tedious gaming part (unlocking everything), the big group of players that bought GT5 solely for the great sim aspect of it can enjoy the full game too.
To be honest, it makes more sense to have a time savers pack for GT5 than for burnout...