Well, for starters the PS3 is only $500 (the $600 version is a premium with wifi and various media card readers, 60GB instead of 20GB HDD but thats upgradable). Both have HDMI, wireless controllers, HDD and blu-ray out of the box. Unless you need the wifi I don't see why someone would spend an extra $100 on the next system up.
Also, the gap between PS3/X360 and Wii is pretty significant from a tech standpoint. Wii is more a Gamecube 1.5 than a next generation system, which was Nintendo's intentional choice as its just not profitable for them, a dedicated games company, to get in a hardware pissing match with two of the world's largest tech companies.
I'm looking forward to the Wii, but it won't satisfy my need for a next gen video game system. A large part of that is its max. resolution is 480p, while PS3 is 1080p and X360 is 720p with an upcoming 1080p firmware upgrade (but it can only be done through VGA or component, no HDMI in the system). For someone who will soon own a nice big Samsung or Sony HDTV, thats pretty relevant. If I drop $2G's on a set I can manage a couple hundred more on a video game system that takes advantage of it.
All three consoles will have some type of downloadable arcade, though Nintendo's is likely going to be the best with its library of NES, SNES,and N64 games all small enough filesizes for quick downloads. They also plan to have downloadable Genesis, MegaDrive, PC Engine, etc. games. But that compares to Sony's plans for downloadable PC Engine and MSX games as well, and Sony is going to offer downloadable PSX and PS2 titles, along with PSP downloads for those of us with the handheld.
Personally I don't plan to keep my launch PS3, its going straight to Ebay. Ultimately I'm sure I'll own all three systems, I'm a hardcore gamer and have always found a way to get any viable system on the market. But this generation starts with PS3 for me because it delivers a host of HD content that will make my upcoming HDTV purchase much more worthwhile. Most notable among them being the full Yellow Dog Linux distribution being released around launch for the PS3, complete with firefox and openoffice. A simple download of VLC and attaching a large external HDD (I have an 80GB already) and I'm on my way to having a $500 kick ass media center for all my HD content. Now I just need to find a good USB based video input device so that I can rip my DVR stuff onto my PS3, like Broncos games.