A couple of reasons really. First, the speakers you show arent magnetically shielded, so if you set up the center channel anywhere near your monitor, you will ruin it. If any of the satellite speakers are anywhere near your case, it could ruin any of the components inside of it.
As is the case with most recievers, their wattage is exaggerated. Im sure the 5.1s would provide more power than this set you show, certainly the sub. The Sony set has a 50W sub, which only goes down to 40hz. The Klipsch 5.1 sub goes down to 29hz, and gives 200W of real power.
You would probably have to spend at least $1000 for speakers AND a reciever to get better quality than the 5.1s can provide.