Primarily for wake vortex reasons, for conditional crossing clearances (after the landing <insert a/c type here> cross runway 27L) and so that the rescue and fire services know what they're heading for in the event of an incident (the a/c type is passed to them as well should the crash alarm need to be pushed).
Maybe other airports are just happy to take their chances that the data they have is correct, experience on a daily basis shows it isn't always so. Here's hoping they don't stuff you up the arse of something on the approach thinking it's smaller than it actually is... how's your unusual attitude recovery skills?
For a couple of seconds worth of r/t the cost in time is worth paying.