It's certainly better from a marketing perspective to say "We have 100,000 apps" than 1,000. I'd be curious to know what a prospective first-time smartphone buyer thinks, perhaps their conception might be that it's 100x better.
They won't think that when buying their second smartphone though.
There are nearly 1,800 apps available for download on my Pre. It is not 100,000 but it is not small either. From what I have seen the vast majority of the 100,000 iPhone apps are spam apps (useless or glorified rss readers), but even if only 5% of the apps not spam, 5,000 quality apps is a good thing to have. Palm's 1,800 is more than Windows Mobile Marketplace.
For sure a lot are spam apps. If people just submitted 5,000 public domain books and 20,000 feed readers it wouldn't make their app store any better. Throwing around large app numbers is meaningless, people should be talking about the apps that they think are quality and aren't available elsewhere.
They won't think that when buying their second smartphone though.