The really, really funny part: if more amazing games come out for the Xbone, someone somewhere will say it's because 720p is the superior resolution (in a "look, proof my insane theories were right!" kind of way). In the end, really, quibbling over what the damn games look like shouldn't matter, it should be, "yes, but what GAMES are coming out for this thing?"
I work in video--the difference between formats exists. 1080p takes more space (them gigabytes), requires data be sent a different way from 1080i (not really applicable on consoles, but definitely a thing for TV streams), etc. It's similar to 720p in terms of data sent (needlessly complicated because old people run everything), but 720p has less of itself by its very nature than 1080p (dem files be of different sizes when using the same compression format for both). So, yes, for good TV's, the difference will be noticeable. But really, it should be: Is this game formatted better for this machine? Is this game exclusive to this machine? Will I notice/care when using other (non-game) apps? (Spoiler alert: Most video equipment I can think of does 720p50/60, 1080i25/30, and PAL/NTSC primarily. Stations might support 1080p streams, but it's not the standard yet.)