My group held the philosophy that you should always have an 18-always be the best at something, so I learned D&D on that philosophy.
I have gradually lowered the (still high) power level in each of my campaigns, but still, when I design characters I feel foolish if I can't get an 18 in something (most D&D games I've played in haven't been with rolled stats). D&D is a fantasy-it should be larger than life. I could live with 16s for some characters. It would be a real stretch for me to play a character whose highest ability was less than 16. I could see doing a monk or other huge MAD character I suppose-in this case, having rounded but not especially high scores is exceptional enough.
With casters, it matters even more. A barbarian with two less Str has 2 more Dex or Con. A wizard with less than 18 Int? If you have a point buy it would make very little sense mechanically not to power up your all-important casting stat as much as was feasible.
In a low power game (Cthulu is a good example) I would feel a little bit differently.
Of course, we're usually playing games on a pretty epic scale. "Save the world" not "find the goblin bandits". I sometimes wish I'd started D&D with a lower power level but I didn't.
BTW I take the same philosophy in real life. I hate anything even close to "normal" or "average". I think everyone ought to be exceptional in some way.