Elliot,
Getting rid of spam is a HUGE benefit. Heck. What I've found
so amusing is that people seem to upgrade their Microsoft systems just
'cause, with no perceived benefit, but merely protecting from Bit Rot.
Many folks update their MS software (Linux, too) in the hope they will get more
stability / more security / more seatures - not becaue of bit rot. Updating
mail clients does not seem to be a huge deal - manypeople update their OS /
browser when prompted. Majority of my friends & family use a web browser to
access private mail. Companies would have interest in upgrading, if it helped
also with viruses & security.
John