I didn't see anyone address this from the service provider abuse
department perspective. I think larger ISP's got sick and tired of
dealing with abuse reports or having their IP space blocked because of
their own (infected) residential users sending out spam. The solution
for them was to block the spam. The cheapest/easiest way to do this was
to block TCP 25 between subs and the internet, thus starting a trend. If
587 becomes popular, spammers will move on and the same ISPs that
blocked 25 will follow suit.
A better solution would have been to prevent infection or remove
infected machines from the network(strong abuse policies, monitoring,
give out free antivirus software, etc). Unfortunately, several major
players (ATT, for example) went down the road of limiting internet
access. Now that they've had a taste, some of them feel they can block
other ports or applications like p2p (Comcast), Netflix (usage based
billing on Bell, ATT, others).
Unfortunately, I don't see the trend reversing. I'm afraid that Internet
freedoms are likely to continue to decline and an "Unlimited" Internet
experience won't exist at the residential level in 5+ years.
--Blake