7200rpm hard drives only drain your battery life by 4 minutes compared to 4200rpm and 5400rpm hard drives. The reason it's so low is partly because it loads things faster and doesn't require the extra power needed for longer use.
I've been waiting on the 100gb 7200rpm Seagate laptop drive for awhile, they've been saying they're coming out with it soon since last year. I called Seagate and they said either this summer or later this year. I think it must have design problems or something for them to delay it this long, because their 5400rpm 100gb version has been out for awhile now.