i had this problem too. here is the solution:
-when people quit out of matches, your stats say you won
-when people quit out of matches, your ACHIEVEMENT stats are not affected (doesnt count as win or loss)
-if YOU quit out, it counts as a loss on your stats
-if YOU quit out, it DOESNT count as a loss in terms of achievements...
this means that even though people quitting out doesnt count towards your streak, you quitting out doesnt count as a broken streak either. i found this out a long time ago, but didnt know if i should mention it in case it encouraged people to rage quit... but since everyones doing it anyways, why not.
i found this out because when i was first going for the achievement, i won 8 in a row, then 9th person rage quit (counted as a win in stats), then beat the 10th guy... i figured out the rage quitter didnt count, so on my 11th match, i was about to lose, and i was SO pised off at the time because of that rage quitter, that i rage quit myself. i kept saying F'n rage quitter, ruined my streak cause hes a b***h, etc. but then i played another match, won, and BOOM got the achievement...
hope that helps