It's not really the email traffic they are after it's the web traffic. I noticed this phenomenon a few years ago after mistyping microsoft and coming up with an ISP offer. It's really quite a smart, low cost, low maintenance way of getting the maximim number of hits possible to your web site. Just think of it in terms of Microsoft and how many hits it gets per day. Then how many typo's there were and how many would hit a single letter swap. You probably got yourself about 1000 hits per day right there for $29.95 registration of the domain.

Yeah, they probably are picking up some mistyped email for Microsoft too if they have mail for unknown recipients forwarded to the postmaster's addy for example.... But what are they gonna get? 50 emails a day from complainers..... I have $5 says they ignore any mail for the misspelled domain after the first couple of weeks.