A DS game can probably be made in 6 months with a 3 man team, which would mean half of your 105k figure. Actually, the quick turnover of the DS from announcement to reality and the speed with which software has been put out for it seems to confirm this.
But I agree with you that not every game is going to come in at this figure, but you know, 50k today ain't what it use to be in the 80s. That said, Nintendo's concern over the average game costing in the millions to develop and everyone expecting it to have the best graphics, best sound, best story and requiring it to sell upwards of 200k copies is well grounded in the reality of industry economics.
Simply put, not every game is going to sell in those numbers and sometimes, games will just bomb even with big budgets. The desire, and I would argue, the NEED, to scale down budgets and still make interesting, fun and entertaining games is a very important part of the gaming industry.
Games is a new thing, relatively speaking. We've been used to every generation producing better graphics. The technology has kept pace, but the costs simply have not. Had productivity of your average team kept pace, we should still be able to make the most amazingly beautiful game with the same sized team that put together your average game in the FamiCom and SuperFamicom days. But that's no longer the case.
This isn't a rant against the Halos, and Zeldas of the industry, I think those have their place and the industry's maturity requires blockbuster releases with development costs of that magnitude. But as far as where Sony wants to take the industry, versus where Nintendo wants to take it, I see more wisdom in Nintendo's decision.
They may be rooted in the Japanese industry's needs and the reasoning may be opaque to many here at GAF, but ultimately, what is good for Japan is still probably good for the rest of the world, even if Japanese developers have seen a relative decline in their influence.