@ webjunk that's a really good question.
We are working on a project for a client and they are using "Mailing List Provider" as their mailing list service, already has an established list and does not wish to move to anything else.
PHPList is a very good piece of software. I have used it in the past. But I also like Interspire Email Marketer (IEM), its not free, but it is very good worth the money.
The biggest reason I personally no longer use PHPList, IEM etc is because of the high time consuming of developing a positive IP reputation and the other on going headaches associated with manging and keeping the SMTP IP off the many BLACKLISTS. It can be a full time job in order to make sure the maximum number of emails go out. So that is the focus getting the maximum # of emails into in-boxes. Thus I would prefer to let someone else handle those hassles and spend time in a more productive area.
Any way you ask a great question.