I agree that a learner doesn't need a professional guitar, but if they can afford one and actually hear and feel the difference, I don't mind them buying what would be better off in the hands of a professional.
Same with photographers - if your photos suck with a cheap camera, they'll suck with a good one.
If we're talking violins, that's different. Beginners and even experts can completely **** up a violin depending on what genre of music they play on it.
Yea, that is one great thing about guitar - you've a lot to work with and endless hours of entertainment, even in the inferior products. I've never been able to pull out my guitar for "just 15 minutes" of practice.
Don't need to be an expert typist to benefit from a good keyboard, though. Although, how often you use a keyboard does correlate to returns on those benefits.