Not the dealbreaker, but certainly a factor.
It is more accurate to say I definitely would have replaced my existing phone if there had been SD card support.
I somewhat agree with Darth Spock that they should leave it if off if it means they could add other features or lower cost, but they didn't do that, either. From what we've seen, it's the 2013 Moto X with 2013 flagship hardware. That's not bad, but I don't see what we gained by not having the SD card.
(Okay, I can think of one scenario: Android SD card support is broken. Motorola wants to ship stock Android so, rather than fixing SD card support as the other manufacturers do, they simply don't include support. This allows them to release updates faster, which is a feature. All conjecture, of course...)