1. The Virginia class was first commissioned in 2004, with a 33 year design life. The XBox 360 was first shown in public in 2005, with a design life of ...? Yup, it's consumer electronics, with a design life of much less than 33 years. Even though there are on the order of 80-100M of them in the wild, by and by XBox 360s and replacement parts will be getting scarce.
(If you think this is an exaggeration, consider the availability of spare parts today for a computer system commissioned 33 years ago, in 1984 — an original IBM PC XT, perhaps, or an original Macintosh, both of which were manufactured in — for the time — high volume. Things like 5.25" floppy disks, or a replacement M-series IBM keyboard with the original DIN plug, were once ubiquitous, but today they're rarities.)
2. A second concern is that these days everything comes with an embedded processor and an enterprising hostile entity might try to sneak malware on board a fast attack submarine via the periscope controller handset. (I've no idea what form such malware might take, or what it might accomplish, but that's not the point: it's that using cheap commercial handsets widens the threat surface of the submarine's sensor suite arbitrarily.)