I have a couple of ideas:
1) They are sending code... only read the upper (or lower) case characters.
2) They are suffering from some neurological problem... that only shows up when you sit in front of a computer for 19 hours a day.
Also (for extra BONUS points!)... Why can?t hackers spell! Is it the same neurological problem that affects their ability to distinguish between upper and lower case letters?
When did ?u? become an acceptable substitute for you? ?b4? is even crazier; it has a digit in there!