That thing's been around since a few weeks after _Panther_ was released (was named WinExpose or something, then renamed at the request of Apple). I don't think Apple did or does something against it now. If at all, it seems they kinda like the flattery.
Who cares about this. As Long MacOS X have buildin. While PC user have to buy this. So what.. Let PC user spend all $$$ on copycat of MacOS X. We just simple laughing at them and watch them become broke.
My PC colleague bought that when it was first announced. It was very buggy and caused quite a few system-wide problems, so he deleted. Also, it didn't quite work as well or as smoothly as the native Expose. I imagine it's been improved since then though.
One thing is for sure, you can bet your bottom dollar that Vista will have a version of Expose built in. It's good not to steal.