I do actually think it's different for different subjects, especially arts and social science ones. There is a lot more interpretation going on and concepts to get your head around and as a result some students might feel the need for more tutor support. That's at least the feeling I have gotten from my fellow students, especially in tutorials. That's not to say maths is easier in any way though!
I think generally most of them try to be helpful but because it's just seen as a bit on the side for them they generally don't spend a whole lot of time on marking, engaging and what not. I do think that's a bit of a weak point. My tutor is lovely, teaches at a college, but she does take about 5 days to answer emails. I do think you could get a hell of a lot more support at a brick Uni (having attended two and working for one that was my experience all the way) but then again I guess the OU would say it's designed for self study.... Disappointing considering the price of it all.