I would have to agree with you. It is not last.fm because there is no scrobbler. What would really be interesting is a scrobbler that worked across all platforms including browsers. As far as I know Boxee's solution forces you to use their software to watch videos if you want to have them scrobbled.
I believe that last.fm works because it scrobbles what you've listened without you ever noticing. Having to manually mark an episode as "watched" is a big hassle and will never work well.
So this is a good idea, that implemented some nice features but that is not solving the main problem. Boxee solves that problem but misses these satellite features.