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With what looks like a very good release of TSW would it not be wise for GW2 to postpond release until say end of September, that will give a full clear month after the free month you get with TSW.
Bearing in mind that GW2's main income will be from box sales they would want to maximize the opportunity and look for an ideal release time, so soon after the release of TSW could prove very damaging for the box sales.
With time a lot of players will get GW2 but releasing so soon after a good releasing AAA title can not help intended sales, they have waited this long another month cannot hurt.