It is testing methods like that however that leads to being released for only one arch. They get to a point where "Hey the 32-bit version is good enough to release, let's release it and we will get to 64-bit with the next point release.". The unfortunate part is they rarely, if ever, get around to it. The other issue is that it gets to a point where they may have to start "undoing" code they just developed because it works in 32-bit but not in 64-bit leading to wasted development time and resources.
Just picture what the kernel would look like for example if they did all the 32-bit code first and then once that was completed started the 64-bit code.
Adobe may be misapplying Agile Development practices, maybe not. You can't tell unless they do end up releasing a final, 32-bit only version. But until then what they are doing fits into the Agile Model.