I can see where you are coming from, for me though it isn't really a big deal. I store all my MP3's on my W7 HTPC/Media server, and it streams it to everythign I own, my other PC's, my TV, my 360. I transfer MP3's to my phone so I can listen to music in the car and not have to stream over cellular and rack up data. MP3 players are starting to die out it seems, other than the iPod. I personally don't see the point in having my music on my pc and on my x1 at the same time, when streaming will serve just as well and not take up space in the the HDD. Also we don't know what kind of apps will be on the X1..if there is a Plex app I will be in heaven
Best media server software I have ever used.
Also, it should be said, that while they stated the X1 will not store MP3's I don't think this pertains to the external HDD support that will arrive eventually. So if you cannot get DLNA working on windows (if you have 7 or above it shouldn't be a PITA, lots here could probably help) then you could probably easily just store them on a extHDD and play them on the X1 from there. I wouldn't compare this to them saying it wont playback from media devices mostly because I think the reason for that is the format of the media player is probably not NTFS (or even Fat32).
Obviously they as a company, like Sony, are trying to expand their music service subscriptions, but for me personally DLNA is a huge feature for media. If Sony doesn't eventually bring it then that sucks for PS4 users (I know they said they are looking into bringing it, but still it may never materialize)