Apple's business model is intended to incentivise everyone to upgrade (remember the days when you had to pay for OS upgrades?) and so for developers to need to support fewer OS versions accordingly. If 90% of your users are on the latest and greatest, that's where you should put your development effort. Beta versions of each release are available for months in advance of full public release so that developers can test their products and remove bugs before the new OS version goes mainstream.
So it is a bit sad for developers to advise not moving to the latest OS because they don't seem to be able to get with the programme, if you pardon the pun.