Well, I'll be honest: DOTA2 hours are kinda bullshit. Most matches go 25 - 35 minutes or so. However, Steam rounds up your time spent to the nearest hour. So even if a match is 25 minutes, or so, it seems to increment hours spent upwards. It doesn't keep a true running total down to the minute. Don't think this is to bloat hours or anything screwy, just they may have assumed the time spent is just a feature that doesn't mean anything (until now.)
Pretty shameful, I have to admit.
Not saying the person above didn't spend all that time playing, just that in my case, my numbers are up there even though I'm a casual noob. I have 400+ hours on DOTA2, still suck, all about 30 minutes at a time. The 100+ hours I have in Fallout NV is most likely at least 100 hours, about 3 hours or so at a crack. Most RPGs are not consumed in 30 minute increments, but hours or more (which is why I can't finish anything right now.)