I think the reason why an XPort SNES emu is so appealing is the limitless configurability on offer. XSNES9X still has little niggles like the inability to disable the throttle on individual pads, the fact that you have to resize the screen without any numerical size data to go on, the lack of per-game configs that would, among other things, allow each game to remember which peripheral it should use (Multi-tap, Superscope etc.), lack of network support (even though I don't use it).
Emulators on the Xbox have become so polished that perfection is no longer just about how well they emulate the systems in question. How well they can be tweaked to each personal taste is now a major factor. In this XPort has set the standard and until that standard is met by XSNES9X, you will obviously see requests for an XPort SNES emu.