The DE and GPE versions of the HTC One may still receive their updates before the carrier edition of the One does, though. I used an international HTC One X on AT&T. It received the Jellybean update months before the AT&T version of the HTC One X did.
So did I, with the same experience. The difference? It was GMS only and not "AT&T ready".
They actually really don't. Apple controls the update process from beginning to end, something that android manufacturers can't do because of the carriers.
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Carriers have been testing iOS 7 for a while now. The difference? Apple won't release it until everyone is done, so no portion of the user base gets it before anyone else. They tried that with the iPhone 4 on Verizon, and the backlash was terrible when Verizon users had to wait about 4 months to get the same update everyone else had.
The testing precedure for users is also very different. When Google is done with in-house testing on the Nexus 4, they send out the update (no LTE or carrier optimization to fool with). It then takes 6 months for anyone else to see it.
When Apple is done with in-house testing, they release a developer preview that you have to pay to use. Six months later, others may see it.
Where Apple excels is small, patch updates. They move those out quickly as long as there is no vendor code involved. Android OEMs seem to take forever with them, although HTC having a 14 hour turn-around to patch the camera on the T-Mobile One was a promising sign.