I agree in part Assassin
I've not seen any relevant study posted showing that green drives don't last as long for HTPC or media server usage . . .
There is some info here about the relative HD playback power requirement of current drives Link
An older article on Ars went over this exact same topic 2 years ago, and they even mentioned HTPCs. ars link
However, in regard to the notion that Green Drives are usually cheaper, I think this has changed recently. In my experience with slickdeals, techbargains, etc, I have found the cheapest drives to be 7200 rpm 3 TB Seagate drives
To my own personal use, it has never made much economical since to pay more for a green drive. I thought that all spun down drives use the same power, and I was wrong. It looks like only the green drives use less than 1W, but the others don't usually consume more than 2W when spun down. I have a couple of green drives, and I bought them back when that was the cheapest thing to buy.
The reason I might not want to continue buying green drives for my storage drives would be that I'm a control freak. I like to be sure that it's spinning down when I tell it to and staying that way because I tell it to. I believe that WD green drives are really 7200 rpm, but their intellipower management dictates their rotational speed on demand (somewhere between 5400-7200, but usually 5400 I'd guess). To achieve the lower power usage, they use more aggressive APM settings which spin down whenever the drive determines. There are tools that let you control APM settings yourself, and I'd rather go that route. I really don't mind the extra heat for the 2-3 hours of usage as long as I can control when it spins down. The only drives I've read people having trouble with effectively spinning down using various softwares (hdparm, hddscan) were green drives (Samsung Eco and WD)