This can be handled to some extent, because everyone can add-on these features, but it can intimidate buyers. Looking around the accesories, the hard drive add-on, the wifi addon, the hi capacity optical add-on, it's expensive, and you don't know if you need it.
IF the PS3 is $350 by the time these devices hit the shelves, there will be a much less confusing option: get the system that comes with all the cool stuff. It feels fully loaded, and it looks fully loaded. A Honda Civic can be upgraded to perform like a BMW, and it generally costs more by the time you're done. A BMW is a simpler choice, and though you have no choice but to buy all the expensive parts that come standard, this certainly about what you get lends a lot of prestige to the brand.
With 400$ consoles, being electronics with all those scary wires, a lot of folks will go for the system that always works with all it's platform's games, always plays the HD movies, always works with wi-fi and all the other stupid stuff.
The PS3 doesn't beat the 360 as things are now. 360's got the games, period. But if we see a bunch of disparate 360 systems that do not always work well together (this is microsoft, they can't even get their own machines to work reliably), the PS3 is going to look a lot more appealing.
I'm pulling this out of my ass, of course. I think if MS is smart they will keep all games on DVDs (the HDD disparity is pretty minimal), and this problem can be somewhat avoided. But MS loves differentiation. They love hitting every single price point they can, even to the detriment of consumer confidence. This new Vista, Office, etc, all share this attempt to gouge for little features that should be basic and in common. Has MS learned that's a bad move? Nope.