To follow on a bit from Dumitru's post - ERPs and others require the topology to be statically configured, generally through e use of a "carrier" VLAN for the ERPs token which is used to form the ring.
MSTP on the other hand caters for dynamic and unexpected topologies (the human factor), because it will converge any topology thrown at it to be loop-free.
There are definitely ways to mitigate against loops in a metro environment so that you no longer need MSTP (shut down non-ring ports, tunnel or filter customer L2 protocols etc), but at the end of the day it comes down to risk.
Cheers,
Ben