For small customers maybe
Especially those with regaulatory compliance issues.
A basic Exchange server for 50 -100 people is quite a chink of change. Still, $500-900 per month, (archive compliance is another $4 per user) over the 3 year term of an exchange server? i don;t know if it really works out...
A shop with 50 people should have an IT guy on staff full time, or near it, or at least an outsourced contractor, so his/her salary doesn't factor in here. Server + licenses + Security + backup, for 100 people, without redundancy, is an easy $15K over 3 years. (initial price plus maintenance and upgrades), and that's likely conservative. Still, the comparrison is vs a 36,000 cost if you include archive support.
For our shop it would be worse, 15K users of which 12,000 require archive compliance going back not less than 7 years. The monthly costs is $100K, and we didn't spend 1.5 mil on the entire solution, across 2 sites (actually 16, but only 2 have servers), will full CCR redundancy across 4 clusters, Tier 1 SAN behind it which we argued was overkill, and point to point replication system to a hot-site with cloud based MX records for hot failover (a geocluster), and even including backups...
OK, maybe this is really for 10-30 users, not 50-100... certainly not enterprise class unless microsoft has some STEEP under the table negotiating...