When current inventory is exhausted you will have no recourse with Microsoft. HP is not pushing the x3 to the masses. It's a business-class phone and as such, they're going to have to provide full support for a minimum of 3-5 years. Companies don't upgrade on a 2 year cycle the way most consumers do. I'll give you an example. You can't download a Windows 7 ISO from Microsoft, you have to go through Digital River. HP on the other hand, still has full software support for my late, lamented TC1100 slate from 2002. I still see a few of them in hospitals every now and then.
Although I agree with everything you say here, in the interest of good information and for everyone's edification, I would like to point out that DR is a company that handles international sales / tariffs, fraud, client and consumer facing versions of storefronts, catalogs, and shopping carts. They also do mostly digital fulfilment, but some physical fulfilment as well. MS is one of many clients of DR, including Samsung, Adobe, Kaspersky, HTC, and many others (Symantec was one of the first and biggest, Blackberry was too at one time).
I say all this to point out that even when you get something from the MS store, you are actually using DR's servers and services - so technically everything comes from Digital River. This is very different from any other reseller where you may buy Win7. At least it was when I worked there 5-ish years ago.