http://russian.stackexchange.com/a/2594
)) is much more prevalent in Russian than elsewhere because to type : on Russian keyboard layout you have to use Shift+6, while on English (US) layout it's Shift+;, which is much easier to type with one hand. So many people don't bother and skip the : when typing in Russian.
Гениальное объяснение, ящетаю.
А что думает ЛОР'овец о причинах подобного поведения людей?