Its not about that at all.
Its about Perin, he just turned 21. This is his first full season in SA. 21 years is very young for a GK. The pressure at Milan is much bigger, the expectations much higher, the fan base is much bigger.. can he handle it week in week out? Or will it burn him or even waste his talent at Milan. Sure he could overcome it all, but I wouldn't risk it just yet. Another full season at Genoa and we can be safe
That being said I would still love him here next season (preferably with one of Agazzi/Abbiati), maybe Perin has a strong character and is a focused youngster and he could handle it all. Who knows.