Roto is definateley harder than H-H IMHO.
Most H-H (points) leagues use a broad array of categories to award points from. Particularly with pitching, I would guess over 90% of H-H point leagues, cannot adequatley take into acount the correlation between ERA/WHIP/ and INN that levels the playing field of your place in the standings in roto leagues.
For instance a BBI or HA both hurt your WHIP in Roto. In H-H leagues it is very tricky to get a scoreing system balanced out that takes into account that kind of stuff.
The difference with hitters is there as well although I believe not as drastic as with pitching when compareing the differences between the leagues and how the actual stats determine your place in the standings.
Similar to the above mentioned example in H-H leagues, a middle reliever can hypotheticaly enter a tie game in the bottom of the 7th with 2 outs and then give up 2walks, 4hits, and then 3 runs before getting the last out. During the top of the 8th that sad middle reliever's team reclaims the lead. He could then retire just one batter in the bottom of the 8th and go on to recieve credit for the win if his team held on to win from there. Most H-H leagues would award points to that middle reliever for the win and unless in a pretty advanced custom scoreing league the owner that used him would end up recieving points.
Now in roto if that were to happen, It would hurt your ERA, WHIP, while only providing help in one category, Wins. There is no positive in that scenario for a roto owner as he was hurt in 2 other categories.
As elaborate as that was there are a billion other instances like that or similar to it that could happen.
Roto is much more in depth and advanced IMHO.
"Son we would like to keep you around here but were trying to win a pennant this year."