Depends which lock you are talking about: bootloader, radio, or SIM.
Dev Edition, Rogers/AT&T model XT1058 have unlockable bootloaders.
Rogers/AT&T radio is not locked. I believe the Verizon version is so won't work on other US carriers. But they will all work on non-US carriers.
And they are all SIM locked, but easy to unlock.
Sent from my LG-E971 using Tapatalk
That is not accurate.
You mention ATT has an unlockable bootloader. Unfortunately the Retail and MotoMaker version for ATT and Verizon have locked bootloaders which can not be unlocked, along with a few other carriers. The codes are not available from Moto's web site, and there is no other path to unlock those bootloaders. The VZW Dev Edition X can have its bootloader unlocked.
As for the Verizon version sim locked and working on other carriers.. The Verizon version (retail, motomaker and dev) is NOT "radio locked" nor is it sim locked, so it will work with a Non-Verizon GSM SIM. Depending on the frequencies of your carrier, the Verizon version will work for GSM/GPRS/EDGE, and possibly work for HSPA/HSPA+, and in some rare cases even LTE can work. It just depends on the bands/frequencies your carrier uses, compared to those supported by the X. I've posted about my VZW X working using my T-Mobile US sim, as have a few others. And I've seen posts of VZW X with ATT sim working.
The ATT version is SIM locked, and you need the unlock codes to use a Non-ATT SIM.
As for all being easy to SIM Unlock, it should be noted that when it comes to the Sprint Moto X, it is sim locked, and Sprint will give SIM Unlock code only if you are a current Sprint Customer with the X on your line/account. No 3rd party places that sell unlock codes have them for sprint moto X. So if the phone is not active on Sprint Service, you wont be able to get a SIM Unlock code for it. But I believe you are correct that any other X which is SIM locked should be "easy" to purchase or otherwise obtain the SIM Unlock codes.
T-Mobile X has an unlockable bootloader. But unlike the Dev Edition, unlocking the bootloader on the MotoMaker for T-Mobile version voids the warranty. The T-Mobile X is also SIM Unlocked out of the box.
I can't comment on Rogers or others.