It's probably more of a case of people jumping on ye olde bandwagon, as per most forums. And so neglecting other possible methods? From my research, the arduino board seems to have been used by a few select vag boffs who have written some source code, themselves gaining kudos and realising some Internet fanclub, allowing most of the bum boys to copy and follow. Giving advice, to further kudos/forum buming... Doesn't mean it is the only way though,
Dturbo GT2259s build thread;
http://306oc.co.uk/forum/thread-3692.html
Daily driver; 330d Msport (doesn't blow up!)