I think bad luck has a much greater shot at helping you lose a league than does good luck have a shot at helping you win a league. I also think that luck is applied differently in roto and h2h. In fact, the best week I've had offensively over the 4 teams I've ever done came a few weeks ago in a H2H league, but I lose 8-1 because the guy had 13 runs, 8 homers, 26 rbi, 3 SB, and a 490something avg. on the saturday night and crushed me. Meanwhile I've had weeks where i've won offensively because the other guy has just had an awful week. However, i consider these examples exceptions to the rule, rather than the rule. More often than not, the best team with the best managing will win. In roto, teams won't be vicimtimized by the same kind of luck thats present in H2H leagues. The team that is drafted best should always win.
Obviously there are exceptions. One is 2003 Pat Burrel, but the biggest is injuries. One kid in one of my leagues has sosa, marcus giles, richie sexson, bill mueller ANNND 3 of their 4 REPLACEMENTS on the DL right now. Thats just crappy luck and luck will effect him more than others. I still think though that the best managers should be able to manage themselves around injuries and thats how you remove luck from the equation. I have Nomar, Garret Anderson, and Kerry Wood and I've managed to keep myself only a half game out in my H2H league because I've made good deals at good times and the chances I've taken have paid off when I've played the matchups right. Now my guys are healthy and I'm poised to grasp the lead which is rightfully mine!
Basically it just comes down to...luck is present but you can get around it if you research enough and respond in good fashion and timing to your injuries. You can also be successful by not drafting proven injury-prone players like Kevin Brown (d'oh) to minimize the chances that luck will attack you.
So theres my answer. I've got more to say but I want to get out and enjoy the day!
Rest in peace Mitch Hedberg. I name my fantasy team "Buoyancy of Citrus", in your honor.