Is the benefit of getting your app out on multiple platforms faster worth the downside of having your app be a shitty citizen of every platform unless you put significant effort into platform-specific tweaks that make it not suck? The cross-platform editors that are the most obvious rebuttals to my observation in the last paragraph are Emacs and Vim, which have cross-platform cores with platform-specific GUI code. It seems like, if being cross-platform is important to your product/team, that old-school approach will nearly always get you much better results.