I think a shared look is important, but a shared feel is more important. That's where the real problems often start. Does your editor know my custom dictionary? Does it have the standard key bindings? My overrides? If the need arises, can I use user interface scripting to drive it?

Also, look can be annoying. If, IMO, my favourite font looks ugly in tool X, I'll have to spend hours finding a replacement (yes, that replacement won't be better than the default or than what I chose after three seconds, but it takes hours to admit that/adapt to the idea that that font is OK)

And yes, Xcode, Visual Studio a d Eclipse aren't the ideal son in law, either, but that doesn't mean we cannot bash other would be sons in law.