Or people like me who just runs their own email server on a dsl or cable line.

Doing the same, see lower.

Maybe that's why some of the ISP's are trying to force everyone to use their SMTP servers. Ameritech seems to be moving in that direction, or at least I can no longer email anyone with an ameritech address, as the ameritech servers reject it with a "use your local smtp server" message.

Or they have your IP listed in a block of "Cable/DSL" and reject mail from there as suspected spam. (Not everything is done for surveillance, even if it is the side effect.) I had a brief correspondence on this topic with RoadRunner, who was refusing my mail for this reason. The workaround was adding a rule to the smtproutes file, routing the mails for *.rr.com through another server in my care, which is on different IP block.