Weren't <img>, <li>, <ul>, and <ol> experimental, non-standard features added by Netscape? Due to Netscape's dominance, everyone ended up implementing them.
I'm not saying non-standard features are always a good idea...but is everyone always waited around for standards bodies to come up with new things, we'd never see any new features.
OK, NCSA was wrong to add those tags to Mosaic without going through standards channels or making them "experimental" and accessible through explicitly temporary syntax. However, I have not seen any evidence (much less the hard proof we have as Microsoft is concerned) that they added those tags with anticompetitive motivation, especially considering that Mosaic predated the browser war.
I'm not saying non-standard features are always a good idea...but is everyone always waited around for standards bodies to come up with new things, we'd never see any new features.