I'm sure that lots of less reputable companies do this. Having used Fasthosts in the past I wouldn't go back if you paid me.
I noticed this behaviour on Fasthosts because it is not how 123-reg does things. I.e. if you disable web forwarding and delete @ and www A records on 123-reg, they do not show a page of affiliate links on customer domains purely used for email.
My workaround was to set up web forwarding on Fasthosts and direct web traffic to an non-existent domain (hacky, but it works).