The only time that I hear people complain about or mention these differences are when there is a big skill gap. Whether I'm playing SC4 or Halo 3 (don't say it) online, I always get mixed reactions and it's usually the same for both crowds.
Competitive or hardcore players (consider myself hardcore due to lack of tourney exp) seem to enjoy playing against opponents who are at/near/higher than their own level. Yes, some of them like to go around destroying the lesser skilled or casual players, but they don't get any respect from other good players. I myself love to have a challenge in both games and I tend to play more games against people that I know because they have the same mindset. However, I do like to go mess around in matchmaking or just join random rooms in SC. I have fun either way, but I prefer to play more competitive games against skilled opponents. To me, that is more fun and that is my preference. Getting better at the game is what is fun for me, but that is what separates competitive and casual gamers in general.
Casual players tend to only care about the aesthetics/sound/graphics/story of a game instead of the actual gameplay mechanics. When I play against these kinds of players in Halo 3, most of the time all I'll hear is "Get a life", "You play this game too much", "Go get some pussy", etc. I've never understood that mentality. Like it's not possible to be better at the game than someone else after playing for the same amount of time. I don't sit here and study either game all day or even for a couple of hours each day. But, I do read up on some strats, and I actively try them when I do get to play the game. THAT is why I've gotten better. I don't just screw around 100% of the time when I play, that's the only difference. I already have my degree and have been working in IT for 4yrs now. Single, no kids, work out 4 days a week, go out, work on beats and videos, and do other things. Yes I have a life, but I do like playing video games, too. They don't seem to understand that and that's just retarded.
I don't knock casual players for how they play or approach the game. Just don't knock me for wanting to be good.