Apple did not drop support for any devices with this release.
i Phone OS 2 was compatible with all i OS devices released up to that time.
Major new i OS releases are announced yearly during the Apple Worldwide Developers Conference (WWDC), and are usually released in September of the same year, usually coinciding with the release of new i Phone models.
The current stable release, i OS 11.2.5, was released on January 23, 2018.
i OS 6.1.6 is the final release supported for the i Phone 3GS and i Pod Touch (4th generation). Apple announced i OS 7 on June 10, 2013 at its annual Apple Worldwide Developers Conference (WWDC) event, and it was released to the public on September 18, 2013 alongside the i Phone 5C and i Phone 5S.
With this release, Apple dropped support for the i Phone 3GS (due to hardware limitations) and the i Pod Touch (4th generation) (due to performance issues).
All other devices from the i Phone 3GS onwards; the i Pod Touch (4th generation) onwards; the i Pad 2 onwards; and the i Pad mini (1st generation) are supported.