I wonder if it has anything to do with a prohibition on fully spelling out G_d as some people do. I'd like to know any biblical references pertaining to that - gotta have a "controlling legal authority", don't cha know? If there is a basis for not spelling out G_d, then one could easily make the leap that "X" would also be appropriate for His Son. Personally, I spell them out.
Deuteronomy 12:3-4.
The thinking is, that it is commanded that the name of the Lord not be destroyed. Therefore, writing the Name on any ephemeral substance (and what's more ephemeral than a computer, which writing disappears once power is removed?)* violates that law.
*Of course, one could counter-argue that the posting database still remains. One could then counter-counter-argue that 1. there's no guarantee that the database will remain forever, and 2. it doesn't matter whether or not the writing is a copy - any instance of the written Name must be preserved.