Nedgame (and, apparently, other retailers in Holland and Spain) aren't happy with the console's price, believing it to be too expensive to bother stocking. A beef, then, but not their main beef.
No, their t-bone is the system's lack of a UMD drive, which they feel robs the store of their main source of income; namely, the mark-up on game prices. With PSPgo games bought directly from Sony via the PSN, and the console more expensive than the existing one, it's not hard to see their point.
Biggest Dutch retailer boycotts PSPgo [Eurogamer]