At least there it's not really any different than shipping a WPF application that's tied to Windows. It's a desktop application, people are used to desktop applications being vendor-specific. I don't like the idea of people getting used to web apps being vendor-specific though. That's not okay. We have a chance to make it right this time. If it runs on your desktop and is vendor-specific, that's a shame but that's expected. If it runs in a browser and is vendor-specific, that's setting a bad precedent that we worked for years to overcome with IE6.
Of course, that's just my personal philosophy. Everyone is different.