This has to be one of the childish and laziest things I've read in a long time. Seriously, who can't spend 10 minutes writing up a cover letter? If you can't even manage that, how the hell are you going to do your job properly? You're not!

Job hunting works both ways. If the company has put in the time to write up a decent enough job listing to make you interested, then you damn well do your side and don't waste their time (yes, this may be a shock to you, but sending a crappy email without a cover letter wastes someones elses time).