Hi Gang,
I think that both of the companies have done a major disservice to the Zip format. They should have at least changed the format extensions to ".PKZ" (PKWare) and ".WZip" (WinZip).
However what this really is, is reason number two that the zip format is dwindling We'll all be using 7-Zip another 5 years anywhow so in a certain sense this doesn't really matter. Also as far as the integrity of the zip format goes, almost no-one ever encrypts zip files anyhow, at least not on download sites so the publicly accesible file format is as stable as ever, it's just not as tight as other formats like Rar and better still 7-Zip.
Also WinRar is a good tool, features better compression, and encodes in multiple formats. However it's a pro tool and is far too litered with features to be easy to use for the average Joe. Simplicity is the main and perhaps only advantage to WinZip. Although personally I think WinRar and everybody that else that doesn't yet support .7z needs to get their shit together or miss the boat entirely.
(just watch some genius will post and say .RAR is better without ever even having tried 7-Zip :))
Cheers,
Christian