I think every game system encourages general (not specific) types of play.
D&D, with an emphasis on XP, levels, feats, and equipment, encourages a certain type of powerplaying -- get the most stuff, so you can get the most points, so you can get the most XP, so you can advance in levels and get more feats. This pushes players to think in terms of immediate rewards and where you character is going next level. This is not bad, it just is something more or less built into the game.
As a counter-example, take Champions/Hero System. Since even equipment costs you character points in that game and since experience produces, at best, very incremental changes, the emphasis is on the character creation and getting the most bang for your buck at the beginning of the process -- experience hones your initial concept rather than builds hugely upon it. Therefor your character, though not really static, is pretty well set along a given path early on. Again, this is not bad at all -- it is the way the game is devised.
Then there is Ars Magica. Since the game is set not in days, but in seasons, your characters tend to take very long-term views of development and plans, at least the magi who can easily live for 150+ years; your companions will probably live less long and your grogs are almost like mayflies. For a grog to advance, he has to go out in the field and be active, the only way he can become a better spearman; for a magus to advance, he has to stay in his lab, not be interrupted, and either read or write or create magical items or train his apprentice. Thus depending on which character is being played at any given moment you have totally different desires for the type of campaign or adventure you want to run and vastly different goals. Again, this could be good or bad, depending on desires, attitudes, and campaign style.
That's just three examples. You could say all three systems encourage "powergaming", but it would mean something slightly different in each case. In the RPG community there is generally a split between those who are really into Rules As Written and those who are into the Spirit Of The Game. The first group gets the labels like powergamer, munchkin, wargamer, rules lawyer, roll player and the like; the latter are seen as closet LARPers, weirdos, GM-hogs, drama queens, and the like. But in the end you need both types to really keep gaming going. Any group will have elements of both -- in the end it is the particular mix that you enjoy that is important to the smooth functioning of the group.