Windows 7 would suggest you're dead wrong about this. W7 is largely Vista with some polish and a rebranding.
They made a great move by consolidating to their Server kernel. Windows 7 reflects this in its speed and stability.
http://msdn.microsoft.com/en-us/windows/hardware/gg463415
MS has also very explicitly said that the W7 kernel is built on top of what they did with Vista:
http://arstechnica.com/microsoft/news/2008/05/ms-no-new-kern...
W7 is nothing more than an evolution of what they did with Vista. Vista and W7 have far more in common with each other than either does with XP.
You are overly negative on Vista and overly positive in Win7. I think you fell for the hype. The differences between them are minor.
http://apcmag.com/microsoft_replaces_vista_kernel_in_sp1.htm
When I upgraded to Lion I experienced a few minor stability issues (particularly with Finder) so I performed a clean install. Have had no issues since. I would be curious to see stability of a machine that has been upgraded from 10.5 -> 10.6 -> 10.7 vs one that has simply had a clean install of 10.7.
[EDIT as I got downvoted presumably for knocking on Vista]
Vista shipped with the version 6.0 kernel. This was known to be a fragmented, "consumer grade" kernel largely based on Win XP. The 6000 kernel build had so many issues that SP1 completely upgraded the kernel to the improved 6.0.6001 which was essentially the Server 2k8 kernel. It was an improvement but too little, to late.