GameRager: Actually yes there is a supposed to, as in if you do your stats differently than the optimal way then you're gonna fall flat on your arse while playing. You want to play 100% your way? Then LARP or tabletop. PC RPGs are pretty fair in letting you go your own way, but due to the limits of budget/time/platform/etc there's never going to be a game where you can do 100% of whatever you want.
klaymen: Pen & paper RPGs>>>videogame RPGs.
As you say, pen & paper games are not limited, only by GM's common sense (or lack thereof).
But on the other hand, there are video games which actually try to be more than "just kill your way to the end", for example the first Fallout where you can go high charisma + speech and related perks and actually you can play it different way as if you were, say, combat oriented. Also there are games where the only role you play is the "I r a mass murderer, lulz" (Diablo and other action-oriented games) and IMO, they are not a RPG by a long shot.
There is a reason I spent half my 2010 PAX playing PnP RPGs, they are so darned fun. If you have an excellent group you can play all sorts of neat stuff. When releasing content for a large audience you have to balance it to the levels at which you expect them to play (i.e. if most of the audience will min-max you need to build a difficulty in for said situation).
Diablo was called an ARPG and I think it's fair to classify it as a specific sub-genre. It basically focuses way more on combat than other roleplaying aspects.
To everyone else:
Well, to be clear, I don't have an issue with min-maxing per se, I have an issue with it when it impacts my enjoyment of the game, for example by making me feel like I hurt myself by not coming up with a complete character build with information off a wiki somewhere or by making me feel like instead of progressing the storyline I need to be out hunting skills (even though I'm more than capable of taking on the next storyline step by then).