Well in all honesty, that is the problem of a player and GM, not of a game. If a game is written in such a way that character depth should be explored and yet GM only encourages tactics and combat, it's only natural that players will only build combat characters.
I think that's incredibly naïve. Players don't build combat twinks because the GM only encourages tactics and combat. They generally build combat twinks despite what the GM encourages, but there is a certain logic behind this decision:
a) Regardless of the game focus, combat is usually eventually present, critical, and one of the few ways to lose control/forcibly retire your character.
b) Brute force is a potential solution to almost every problem (or at least, every problem that impacts the health of your character). Everything else tends to only solve some problems.
c) In general, for any other skills but combat, the party can rely on just one member of the party to have that skill. Having two experts in ancient Greek or Botany is of marginal utility - even if tests of those abilities ever come up. Having two experts in combat however is great utility.
d) Combat skills tend to be the one area of a game in which a player can't partially fall back on his knowledge and understanding as a player. They tend to be far and away the most rules relevant area of a game. To the extent that combat is not the most rules relevant area of a system, and that is really rare, 'brute force' and specialization can generally be applied to whatever area that is.
Since genera's like Fantasy and Supers tend to allow for massive amounts of brute force, and better yet highly controlled and precise brute force there is almost never any gamist reason not to make some sort of very narrow focused hammer of a character and then treat every problem like a nail. These include characters that can take very large numbers of actions relative to the norm, characters that can't be observed, characters that can overwhelm any foes defenses, near omniscient characters, mind-controllers, invulnerable characters, and plain generic omnipotent characters. Characters like this not only have combat 'I win' buttons, but very generic 'I win' buttons. When considering how to allocate points, it's almost always better to spend more points toward being unobservable or omniscient or invulnerable than it is to be a little stealthy and a little knowing and a little durable. This gives you a reliable mode of operation that can't be countered, rather than an undependable chance that maybe you might succeed. An invulnerable character has a way to solve almost every problem just by pushing through it. An omniscient character has a way to solve almost every problem by knowing all the answers. A combat twink simply destroys any problem placed in front of him. Anyone that has played GURPS, World of Darkness, D6 Star Wars or any other number of classes systems knows that there is really no point in being broad. You can in GURPS make a really broad 300 pt. character who roughly corresponds to a well competent real world person, or you could spend the same 300 pt. in the same genera to make a demi-god or at least an action movie hero. You can spread your dots around a WoD character sheet to create evidence of a rich and complex life, or you can do what everyone else does and pick a couple of valuable complimentary general problem solving skills and abilities put 5 dots in them.
Where is this really balanced point buy system of which you speak, and why hasn't achieved greater market penetration?