D&D has levels. A whole packet of relevant stats increase all at once. This encourages playing to gather experience to get to the next level, so you can get higher stats and new toys (i.e. feats, prestige classes, and so forth.) That causes all sorts of interesting play effects. Depending on how you want to play, this may be a good or bad thing. It’s not how I want to play.
L5R has a point buy system, combined with insight ranks (i.e. levels.) Since the cost of raising stats increases as they go up, this encourages balancing stats out to find the cheapest point cost to get to the next level. But balance isn’t nearly interesting as imbalance, so this isn’t how I want to play either.
I haven’t played 4e Shadowrun, but as I remember from the older editions, it simply has experience that you spend for more goodies. Point costs go up as the stats go up, but there’s no “next level” to shoot for, so there’s really no reason not to spend them all on raising whatever you like. This seems decent.
But if the degree of difficulty simply goes up as the characters become more capable, isn’t this sort of like an endless staircase? So…why have character advancement? Why not simply have character change? I may have to track down some systems that do this.