I prefer to think that:
1) Spain just have an irrational hate against the Microsoft brand.
2) We're very conservative and nostalgic here.
3) "La play" is so associated to gaming console it trascended above anyone else.
I doubt your two first points have substance, (the nostalgic part, at least. Damn right about being conservatives) but I can totally relate to the third one. So you do reaffirm my point that people here can't see past Playstation, because that's the "rule of gold".
I do admit that saying "Vamos a echarnos unas xboxs" sounds totally horrible in comparison of "¡vamos a echarnos una play!"