they are not a www firm. that means nothing about what type of firm they are or what services they may or may not provide.
here is my suggestion. don't buy your domain name from the same company that you buy your hosting from.
use search and find a domain registrar. there are many of them and they are all the same service so pick the best price.
then use http://webhostingtalk.com
to do your research about what the best hosing company is for your needs.
phpbb does not require a lot of resources until/unless you get many thousands of visitors/posts etc.
as long as the hosting company provides php and a database that is about all you have to worry about.
and finally, how would anyone here know the answers to all of your questions about why any given hosting company does anything?