The Wii currently is the hottest item on the block. You can't find it in stores at all and it's all the rage on the internets. Early fanboy reports imply that the Wii is the king of the next generation, and that the 360 and the PS3 will just be afterthoughts. Obviously, it's way to early to tell this. However, a more important fact is pointed out by the success of the Wii. Third party developers will be listening and acting on this. The Wii will begin to gain momentum, and business sense would state that this will give the Wii a leg up in size of its games library.
The Wiimote has been sold by Nintendo as the best part of the system. Its motion sensing abilities are part of the number one draw to buy a Wii right now - the ability to play interactive fun games with your friend being the foremost point. It is so important to Nintendo to emphasize this element of the system that just about every game takes advantage of it. It's safe to say that without the Wiimote, the system wouldn't have the character it does. This isn't a knock against the Wii, it's just a point that the Wiimote makes the Wii what it is.
Since last spring, Nintendo fans have seethed over Sony's SIXAXIS controller and its motion sensing capabilities. The fact that it was announced after Wii made everyone suspicious that Sony was out to blunt the effect of Nintendo's Wiimote. This is definitely possible, but has yet to be confirmed. The release titles for the game really did not support the motion sensing capabilities of the SIXAXIS except for trivial game mechanics, such as shaking off an attacker in Resistance. In fact, the most obvious use of the motion sensor was in Fight Night 3, but wasn't used too much at all. The game really could have been an answer to WiiBoxing, but instead it decided to compete head to head with the 360 version, probably because there was less work involved.
And this is the point I want to make. The ability for the PS3 to have that motion sensing capabilities is what will help it succeed. The more developers that move to the Wii as a main platform, the easier it will be to port those games to the PS3. Why? Because the basic game mechanics won't have to change much. You have a boxing game with punches thrown by punching with the controller. You have a golf or baseball game that detects the swing. We are slowly moving towards this.
The PS3 already is starting to make plays in this territory. Flow actually is very fun and uses the SIXAXIS as the main mechanic for moving your character. The Rub-a-Dub game for PSN will also use the SIXAXIS as a main mechanic. Blazing Angels, originally released on the 360 and released in December for the PS3, allows you to enable SIXAXIS motion controls for steering your plane. It's not realistic, but it's a lot of fun. The biggest knock on this game was the fact that the motion sensing was delayed just a little bit. I think this was intentionally done by the developers to take away some of the arcade feel that you get from doing it. However, there's a great level late in the game where you have to fly the plane through a glacier with tight turns and low "doorways" of ice while being timed, and it's hard and a lot of fun.
Yesterday, I picked up MLB 2k7. I haven't played baseball on a console since Super Bases Loaded on SNES way back when. This game is a lot of fun, but I think the batting and motion sensing has fallen a little flat. Instead of swinging the controller like a bat, you thrust the controller forward when you want to start to swing. It's actually quite awkward, and I look forward to seeing what other games will do instead of this. If a game comes out that let's you swing the bat for real, then I'll be all over it.
The takeaway point here is that while Sony might have added on the motion sensing as an afterthought, it's in Sony's interest to focus on the SIXAXIS capabilities, particularly with the success of the Wii. Even though the hardware between the consoles is so different, the fact that the underlying mechanics may not have to be modified much from Wii to PS3 is definitely a point towards PS3's corner versus the 360. Some games just don't make sense using a controller, just like some games just don't do well with the Wiimote (Red Steel, we're all looking at you).
Sony's Harrison said "Rumble is a last generation feature" which was spun as a rejection of the lack of rumble on the SIXAXIS. But it's probably coming, and I don't miss it too much. Hell, does your keyboard and mouse rumble? I've played doom, quake, and half life for years without rumble, and I don't see it making a difference towards the way I play. Motion sensing, however, is the Next Big Thing (TM) and look for Harrison to touch on it in front of the GDC next month.