Enzo Coloni sounds quite cordial about it all:
“Abbiamo preso parte al campionato fin dalla prima edizione e porteremo con noi molti bellissimi ricordi legati a questo impegno. Vorrei ringraziare Bruno Michel e lo staff della GP2 per la loro collaborazione nel corso degli anni”.
Rough translation:
"We took part in the championship since the first edition and will take with us many wonderful memories of this commitment. I would like to thank Bruno Michel of GP2 and staff for their cooperation over the years".
http://italiaracing.net/notizia.asp?id=36364&cat=4
I wonder if it has anything to do with any possible conflict of interest between GP2 and Coloni's Auto GP? Hasn't seemed to be a problem for GP2 that Coloni runs a series which is a potential rival.