Nope, nothing's wrong with the Magic Mouse. But I think Apple is once again migrating its user base (and eventually the entire industry) toward a longer-term goal. My silly wild-ass guess is that the next version of the Magic Trackpad and all laptop trackpads will use an AMOLED touch screen. It could show a virtual numeric keypad, or other control setup, instead of just being a blank trackpad.
Why would Apple do that? To first test user reaction, then prepare us all for yet another evolution beyond that, to a full virtual keyboard. No more physical keys, just a large AMOLED with virtual keys displayed, that could instantly switch between keyboard and trackpad depending on what the user's fingertips are doing. There would no longer be any need to move your hand between keyboard and pointing device. That small motion is a barrier between the user and the computer, and Apple is all about removing those barriers now.
So, aside from making it slightly more convenient, why would Apple want to get rid of a separate pointing device? Because iOS devices don't have a pointing device at all. The iOS GUI doesn't have a cursor, so you never need to use a pointing device other than your own fingers. I think Apple will be gradually moving us all to some kind of Mac OS interface that has many iOS features. Maybe in the Mac OS XI timeframe.
Making small steps ever year is the only way Apple can get there without jarring its users too much. On the other hand, I think the best way to make the next-gen Mac Book Air really thin is to use a touchscreen instead of a physical keyboard. So Apple could just drop the bomb on us when the next MBA is released. Lots of people wouldn't like a pure virtual keyboard on a MacBook, but the MBA isn't for everyone anyway. It's a higher-cost, "executive laptop" niche product, so it has to be on the cutting edge. (My extremely wild prediction is that it could be as thin as an iPhone 4: less than 10mm if Apple can get someone to build a super-thin SSD...)
And one more little thing: AMOLED, when made with very high pixel density, is relatively expensive now, and yields are very low. But if it is used only to display keyboard-sized keys and letters, the resolution wouldn't need to be very high, which could keep costs down. And it would streamline manufacturing because there would just be one keyboard SKU instead of multiple international keyboards with different keycaps and/or key layouts. The international keyboards could be instantly configured in System Preferences > Keyboard.
OK, that was waaay too long. Sorry. (TL/DR).