I think skype was released a month or so after they acquired skype. Besides the skype integration that they show in the next version is way better than on any other phones/OS
Set to be released this fall, if I remember correctly. So it's not that far off.
Skype (when not yet acquired by MS) shelved any plans of producing a Windows Phone version, so Microsoft (after the deal went through) probably had to start at near-zero with its version. At the same time they were likely working at the more native integration for WP8.
Just how many people would you expect them to throw at a problem that likely won't generate that many new customers? It all comes down to that in the end.