Granted. But I'd argue that there are still vastly more skins available through the base game that are, by their nature, much more rewarding to obtain. Plus with how many there are the average player hasn't gotten close to collecting them all yet. Of course I wish they would add new stuff (like they are probably going to in HoT), but all things considered I'd say less than ten percent of all skins in the game are available through the cash shop, and I for one am fine with that.
Besides it isn't like this is anything new, how many skins did GW1 add to its cash shop over the years? Over a dozen at least. And how many were added directly into the game through a means other than a paid expansion? Zero. This is how MMOs work; you get your new "through gameplay" stuff when you fork over the cash for an expansion, and everything else is in the cash shop. So frankly the DOZENS of back skins they've been adding through the living world is technically breaking the mold and going above an beyond for the player's benefit. Arena Net didn't have to give us a single new skin through actual gameplay, and most MMOs wouldn't have.