>Because, all old code will need to be rewritten to run on Win10,
But Win10 is only a marketing label. Remember MS's previously released Win10 release cycle and LTSB, where effectively each LTSB release is equivalent to major version change, which prior to Win10 would be announced as a new and improved version of Windows eg. XP, Windows 7.
So code will need to be constantly 'rewritten' (and recertified in some cases) as MS keep moving the goalposts of Win10 compatibililty.
>I can see CFO's yelling at CTO's while crunching numbers and cursing
Maybe not a bad thing, maybe what's needed are a few Enterprise Linux success and TCO articles in Accountancy magazines...