They aren't, the expose function of them is really useful for graphic design, they aren't meant for little kids playing world of warcraft. Saying that there is a much more comfortable Logitech mouse with programmable expose and spaces buttons now though.
Expose isn't a function of the mouse. Any multi-button mouse attached to a Mac with some software can be configured to launch Expose.
Mighty Mouse is absolutely without a shadow of a doubt the
worst mouse I have ever used in my life. I've used mice that cost me less than £5 and they were better than this. The problem is that it doesn't have a physical button, so it relies on the same technology as a laptop's trackpad to guess where your fingers are.
This means that if you want to right click you have to lift every other finger off the mouse. You also have to lift your fingers off the mouse ball too. It is a total pain and it is not very well thought out.
The fact that it is one of the most expensive mice out there makes it even worse. How can anyone justify paying £49.99 for the wireless version when there are so many better options out there?
I swear, if this was an idea cooked up by Logitech or Microsoft then it would have been killed off a long, long time ago. The only reason it is still in production today is because it is bundled with Apple's machines. If it didn't have the Apple logo I bet none of the people here who are singing its praises would even have tried it.