Blocking outbound port 25 has legit uses, it keeps from being able to submit mail with the only information about the source of the mail being the IP address. Port 25 is meant for MTA to MTA mail transfers. Outbound 587, named "submission" is the port you can connect to at your email service provider to drop off outbound mail. This port is required to support authentication before accepting mail. This provides an additional layer of auditing and access control, and thus a way to easily turn off problem senders, on a per-account basis, should the need arise.

A smart webhost would block outbound port 25 and require you to send mail authenticated through an MTA provided for the purpose. But of course, chances are most people here are not using purely "web hosting services", but rather dedicated machines or VMs that run their own MTAs. However, any decent MTA can be configured to use a relay host and authentication, which is fine unless you're sending massive volumes of email (in which case, why are you sending it from a rinkydink webhost or single VM?)