To get an answer for this question is really hard. I think there are a lot of factors involved in 'the way to the top of the billboard'.
Many of them have been written before in this thread: to be in a big label, to make Pepsi ads (hehehe, really cool one), to appear at MTV broadcast... Anyway, these factors can be resume usually to one: to be in a big label.
To be decent, to do emotional lyrics, etc. I think is not the key to be famous or not, I suppose. There're a lot of emotional lyrics, made of deep feelings and the composer/s are famous, or not.
To be lucky. I think it could be important sometimes. Very important in some cases.
If Anathema were famous I'll say 'never mind'. The most important thing to me is the lyrics/music, the mixture of these elements to get something that make me feel alive. Beatles, for example... never before a band were so much famous, and they did incredible songs. I think fame don't corrupt the soul of the composers always.
So, I love Anathema's music. If they are famous or not... pstt. what is the difference? To me nothing. To Anathema? who knows?