At least in UK accounting a subscription model has benefits for anyone who can claim a Windows licence as a business expense. A subscription would be classed as an operating expense and can be wholly offset against tax as part of the cost of sales. A licence on the other hand is an asset, which can only be depreciated over at best, three years (50% the first year then 25% for the following two)
This has a number of effects: By reducing my costs in the current year and at the same time being able to offset the entire cost improves my cashflow and reduces my tax burden. Also, by avoiding the ownership of an asset I reduce the book value of the company so I increase the ratio of earnings to investment (ROI). The additional cashflow will allow me to grow the business; I should be able to get a good return on the cash or else why am I bothering to be in business in the first place?
It may well be that Microsoft make more money out of my company using a subsription model, but that does not necessarily mean that my company makes less money, it all depends on just how I can juggle the numbers and what I do with the cash.
Disclaimer: I am not an accountant, but I have been a subcontractor running a limited company for several years.