Ubuntu has no control over the Skype project. They aren't obligated to support every third-party product when it is impossible to do this.
That's an interesting attitude.
Backwards compatibility is a generally regarded as a feature. If you read Raymond Chen's blog about the length's Microsoft went to in order to support old software on new versions of Windows you'll see how important some operating system vendors regard it.
Linux generally seems to have an interesting attitude to backwards compatibility. "It works on old hardware" is something that used to be regarded as a huge benefit of Linux.
These days - especially for Ubuntu - it doesn't seem to be regarded as a feature at all. Additionally Ubuntu seems to introduce breaking API changes in every release. I find that to be quite a surprising route to take for an OS that is trying to build desktop share.
I'd be quite interested to hear why people think they do this. Is backwards compatibility just not seen as important at all or is there a bigger strategy here?