Correct there are only a few companies behind all these brands. They operate on the same basis as Procter&Gamble and Lever Brothers with their numerous washing machine powder and liquid brands.
If you want to know who is behind what brand then go to
http://www.internic.co.uk and lookup who is behind each URL. For instance Callax are behind Abroadtel, Phonebird and PennyPhone The very aggressive and ever growing Swiss Finarea is behind Dialwise, Dialaround, Budgetcom, Bestmintes, Telestunt, Telesavers, Telediscount, TopUpNow, VoipBuster, VoipCheap, CheapestCalls 18866, 1899, 18185 and probably a few more as well. Centrica (who owns British Gas) owns Justdial and Ratebuster. Call2Call, Gem-Tel, Sipgate, JoyCall, 123Call, Lycatel, Simply-Fone and of course Skype all appear to be one off separate companies.
Are you aware of
http://www.niftylist.co.uk where you can keep track of which of these brands is currently offering the best international fixed and mobile call prices?