On the main topic at hand: Yes, GT5 does. Whether or not some here agree with that, the people dedicated enough to GT (or even racing games in general) aren't the target - it's the legions of casual gamers that would require the new metal. DLC could make this happen... but after over 9 months since GT5's release, we haven't heard anything concrete about DLC for any new cars (just Chromeline reskins), so the outlook isn't exactly sunny.
Don't get me wrong - I'm sure we'd all love new cars too, not just the casual gamers. But the people who are already in support of GT5 don't need further convincing: new cars would be a bonus. Those people who are looking elsewhere need the incentive to stay. Nevermind that the idea of Kaz' "car encyclopedia" should stretch to include modern metal just as much as it does historic automotive pieces: the former is fairly poorly represented in GT5, as the majority of '05+ models are supercars.
Not sure I agree with you on this one though (the target aimed at that is), sure DLC will grab some attention and persuade a few 'casuals' to start GT5 back up again and perhaps Kaz expects a lot of new casual gamers since the 'announced' DLC roughly seems to coincide with the Platinum edition of GT5 but GT5 as it is right now probably has just about the right amount (some will say more than plenty) of content for someone who only plays casually, aka occasionally.
It's those who play GT5 almost on a daily basis that much sooner reach its limits regarding available content and who are perhaps also more willing to still invest in it.
For someone like me who spends 99% of the time driving Premium cars (love my cockpit view, therefor only use Standard cars for specific online events for which there aren't enough Premium candidates, when I suddenly develop an urge to 4-wheel drift my Jay Leno Tank Car/drive other unique cars or when I'm in a retro-mood
) a few more additions will significantly prolong its lifespan and keep it interesting for me, as there's only so much differently coloured, differently trimmed, differently tuned, etc. variations you can own of the Premium selection before it starts to become a deja vu (purely talking about driving them, each
online race is different and keeps the experience fresh), and that's coming from someone who currently owns about 315 or so Premium cars.
The casual gamer won't have that 'problem' very soon and the new Platinum GT5 customers (whether casual, returning fans or future fans) still have a lot of time to play before they reach that point (and will perhaps postpone the purchase of DLC until then).
And another thing, I too am a casual player of certain games which only kept my interest for a short while before I moved on to another title, I've yet to be persuaded to return playing those games even when I'm aware that since then tons of DLC were added (which obviously I haven't bought).