You are correct with the updates from MS (via Insider or Dev Preview), but that's not the same as the carrier releasing a fully supported version to non-techie customers in bulk. Outside of DEV preview/insider, Windows phone gets stuck in much the same updating situation as many Android phones due to OEM or carrier blockages. Witness how many formerly "flagship" Windows 8 phones, like the HTC models, that won't be receiving Windows 10
The large corporate customer (of Verizon) I work for actually had to threaten legalities over Verizon's holding back the Win8.1 denim update for Lumia 928's. The legal angle was that there were security updates included in the OS update, floated ideas of "negligence" for not releasing the update (which they suddenly did with no pre-announcement near Christmas, finally).