Speaking generically, what displays on the screen may not mean exactly what we think it means.

<channeling Bill Clinton>
Without more details, all I can offer is that different carriers have different definitions of 4G and each tower has specific capabilities (more than just 4G or 3G).
With rose colored glasses I'll say that perhaps the logic to display 4G or 3G changed, not the service itself. But someone might have information from practical experience instead of my WAG.
BTW: No update for me. AT&T (5s running iOS 7.1 b1 if it matters).