Because, FRAPS was Designed (way back when we only had 1 or 2 cores) to help take the CPU bottleneck out of the equation by using lossless encoding (less CPU, but a lot more I/O).
It shifted the resource consumption primarily from the CPU to the hard disk. With the better processors, this is no longer needed.
So, the point I was making - is that if you have a capable CPU, use lossy encoding, which (when configured properly) will still result in perceptibly lossless video, at a fraction of the file size.
Second of all, to do what you propose you'd need some other software. All the other options aren't anywhere near as good as FRAPS. You won't be getting rid of it.
PS. Someone else posted in another topic that the 4GB file size limit is because a lot of video editors can't handle single files over 4GB. That makes more sense