I had a player who always rolled lucky in D20 Modern. (I was a player in that one, too.) He used a lucky D20. He's now a DM, but since he uses a computer to roll his dice...
I have a player like that in my current D20 Modern campaign. I need to police him better, just to be sure.
There was one more player who I know was cheating, however, in multiple campaigns. He would tell us "I so hit that AC!" and, of course, would immediately pick up the dice. So many critical hits! To correct the situation, one time when I was GMing I made him sit right beside me, and his girlfriend also reported on his dice rolls. (He also played a CW samurai - not in a campaign I was running - who valued his swords more than his life. Literally. As in our party risked our lives to save his, yet he wouldn't try to escape because neither of us had his swords. Another reason to hate that class!) He's since been thrown out of the group, but none of us have informed him of this yet.
There was a player in a DnD game who couldn't help but roll a "6". He broke records (probably) doing that. He also rolled above a 10 for Initiative maybe three times in his career (from 1st to 4th level).
And finally I have a player who couldn't make a dice roll to save his life (literally) until he reached 8th-level. No wonder he played a paladin in my DnD one-shot and used a flamethrower in my D20 Modern. (He took an AdC that gives additional action points per use - the daredevil - and, of course, he had the fewest APs when he reached 8th-level. He also made sure he has the highest Defense value in the party, which, unlike DnD, is more than just manipulating your magic items.)
His luck was bad. Let me give an anecdote. I was running Adelie 14, an adventure set in Antarctica, and I usually rotate my dice (I've got about 7 d20s ... they don't all look alike, though). However, this time I just grabbed a D20 and used it. It was rolling really lucky (the NPCs had attack bonuses of +5 and had to hit Defense values of 17-24, but I hit a lot). Meanwhile said player was rolling terribly. (He couldn't use his flamethrower at the time.) So we traded dice. My luck fell, his didn't get better, and any time I rolled his dice against him I rolled high. Good thing he worked on his Defense score!) Even when he rotates dice his luck is always terrible!
Luck streaks happen in every group, unfortunately.