It definitely matters to those who chose the X1 on the assumption that it was their only option. It's a good thing for PC gamers. Kinda stings those who bought X1 on that assumption, and kinda reduces the reason to own an X1.
Which, in turn, means lower X1 sales and a lower number of games (which is already the case). Which means fewer games for those that bought the X1.
It's not really a good thing for X1 owners unless you start focusing on very specific examples (like a multiplayer game with cross-play, which is a good thing). From a business standpoint, yeah, good for Microsoft. From a PC gamer standpoint, yeah, good for PC gamers. For the Xbox One owner, I'm still uncertain how this works out in their favor (per the title of this thread).
All that said, I see nothing wrong with you -- you, personally, or any other Xbox One owner -- loving their system and thinking it's a great system. It's not my bag, personally, but it has far too many games to chalk up as a bad system. But we're not talking about preferences. We're not talking about what we think is neat about Xbox One. We're talking about whether formerly-exclusive games coming out for PC is a good thing for Xbox One owners. And I don't think it is. If the best we can say is "well I don't really see how it affects me" then that sort of makes the point for me. We have enough bright minds on here who are aware of the business and mindshare implications.
Saying "oh well we still get some great games! What's the big deal guys?" on NeoGAF where we have access to a ton of sales data and information seems supremely naive. It means less reasons to buy an X1, which means lower potential sales, which means fewer buddies for you to play online with, which means less incentive for devs to put their game on the system.