a) 6500's are versatile and can be used (with vary degrees of success) for a variety of purposes: switching, core routing, edge routing (not great), load balancing, even IPSec services with things like the SPA modules.
b) They're incredibly power hungry, so the bit about needing more power is apropos.
c) They're still used in lots of places. Ever seen a budget hosting colo? Chances are there's a 6500 there.
d) They're stupid cheap on the used market. The fact that there's even still a used market for the 6500 shows how venerable and long-lived it is.
That said, I do want to stab the first person who suggested using it as an edge router exposed to Internet traffic.
Or that in reality if they were using a p2p CDN the users would be absolutely losing their minds on reddit/HN/etc for using their bandwidth without permission