[dspillett]

People are slow to upgrade database systems, as it can take a log of regression testing to make absolutely sure your applications don't rely on unsupported/undocumented/undefined behaviours that make them compatible with the newest release (or are affected by officially acknowledged breaking changes). Especially in enterprise systems. Even if developers upgrade quickly, their clients with on-prem installations may not. That means that to be taken seriously you need to support your major and minor releases for some time to be accepted as a serious option in some arenas.

Supporting five versions is no more than MS do: currently SQL Server versions 2017, 2016sp2, 2016sp1, 2014sp3, 2014sp2, 2012sp4, 2008R2sp2 and 2008sp3. 2008sp3, 2008R2sp2, and 2016sp1 will hit their final EOL in a couple of months taking SQL Servers's supported list back down to 5 too.

I expect other significant DB maintainers have similar support life-time requirements for much the same reasons, though I'll leave researching who does[n't] as an exercise for the reader.

[greggyb]

2008 and R2 are still in a supported phase of life. It's the "exorbitant support fee" phase. Nevertheless, you can still get Microsoft support for the two after the "EOL". It's more an end-of-public life

[dspillett]

Aye, and by the same technicality you can still get support for 2005.

Similar with PG I assume. You could always pay someone an expensive contracting fee to support your use of an older version than is publicly supported.