MTG needs to have sets finalized 9? months ahead to account for printing, shipping, etc. time. That window is much shorter with digital download products.
Blizzard has also shown willingness to tweak problem cards and refund dust when doing so, while Wizards can only ban a card and make it worthless in tournaments. WotC tends to keep that as an absolute last resort for Standard format (recently it only happens when tournament attendance drops), so they do everything they can playtest wise to avoid it happening.
Now of course they would be playing with newly designed cards well in advance, but not necessarily as far in advance as paper sets need. I would not presume that they had most of the design wrapped up in the middle of Naxx release for example.
MTG needs to have sets finalized 9? months ahead to account for printing, shipping, etc. time. That window is much shorter with digital download products.
Blizzard has also shown willingness to tweak problem cards and refund dust when doing so, while Wizards can only ban a card and make it worthless in tournaments. WotC tends to keep that as an absolute last resort for Standard format (recently it only happens when tournament attendance drops), so they do everything they can playtest wise to avoid it happening.
Now of course they would be playing with newly designed cards well in advance, but not necessarily as far in advance as paper sets need. I would not presume that they had most of the design wrapped up in the middle of Naxx release for example.