Now, after all this rambling, what's my point? Well, why should we concentrate so heavily on interface when we should really be worrying about functionality? The best interface won't rescue the worst program.
All the same, the best program is worthless if no one can use it. Which is precisely why vi and GIMP aren't more popular; both suffer from awful interfaces, even if their functionality blows the competition away (as a side note, the GIMP 1.1 series is doing somewhat better with its interface, now that they don't make almost all of the menus count on a function you can't even assume your user has or has mastered: namely, the right-click).
No interface is intuitive right off the bat. But as programmers, we have a responsibility to our users to flatten the learning curve as much as possible. Interface standards aren't there to "constrain creativity." They're there to standardize interfaces for common, mundane tasks.
For example, let's compare two common Windows programs: Word and Excel. Very different programs, doing very different things, but they do share a few things. Both can cut, paste, copy, and whatever. Both allow the user to enter text, though for different purposes. Both allow the use control over font face, color, size, etc. In fact, these are very common functions that many programs have.
By standardizing the interfaces to these, learning curves are considerably shortened: if I know how to cut and paste in Word, I can cut and paste in almost any program, right off the bat. I only had to learn the interface for these one time, rather than again and again for each program.
But programs also do different things. These are where interfaces start to diverge. But they stick to the standards for mundane tasks, and this is a Good Thing.
Interface standards don't constrain developers. Quite the contrary; they free developers from worrying about interfaces for the common stuff, so they can design good interfaces for the things that make their programs unique. And by doing so, they make their programs easier to learn overall, because a person can jump in and do the most basic things right away, and move on to more advanced concepts immediately.
A hammer, a wrench, and a screwdriver all do very different things, but you'll notice that the handles all look similar. Again, there's a good reason for it.
By the way, the interfaces to any two console games on the same platform, if you'll notice, also stick to standards when they apply. You can normally count on Left to move left, Right to move right, Up and Down to take appropriate actions based on the point of view, and Start to pause and maybe bring up a subscreen of some kind. If you're on a driving game, you can pretty much be certain that one of the buttons on top of the control pad (usually the one closest to your right thumb) is the accelerator, and the one right beside it is the brake. In platform games, the button closest to your right thumb usually jumps; in shoot-em-ups it usually fires. So there are standards even in console games, and yet you find these "natural." You know why you do? 'Cause they were standardized.
What's the fun in being "cool" if you can't wear a sombrero? -Hobbes