I was always under the impression the innovative part of TM's "service" is taking the bad wrap/reputation hit that comes along with extracting more money for venues, artists and (or course) themselves. So essentially being paid to be the "evil Ticketmaster" we all know.
Artists, venues get to blame them while keeping the base cost of their tickets lower (for perception purposes), while still making money on the TM fees.
Good point! The percentage of the ticket price that the artists are getting is - conveniently - never revealed so fans are left to assume that it's evil Ticketmaster gouging them. I see a comment above yours https://news.ycombinator.com/item?id=33290468 that suggests the artists usually get 85% of the profits, and of course we have no way to know.
Artists, venues get to blame them while keeping the base cost of their tickets lower (for perception purposes), while still making money on the TM fees.