Unless what any /. reader observes as realtime data, GTFS Realtime is just not realtime transit data. GTFS Realtime updates a GTFS feed with current information if a planned trip was canceled. It is in its current form not telling the actual positions of busses, their punctuality etc. If you want to look more into why realtime is not realtime, go to their usergroup and search for wave. A nice thread on why Google Wave (aka ProtoBuf combined with XMPP) does make sense here - but too complex for Google and their partners.
Next to that its great that an inferior defacto presentation standard is send into the world as 'cool and amazing' but the only reason Google is pushing this is because it is simple. It is not like SIRI, NeTEx, Transmodel, etc. that every operator out there has running in their management systems. What Google did with GTFS was: lets materialize all possible data. Tell operators that their timetable generation is wrong. Let them fix timetable generation. Use timetable and a networkgraph to do some routing *advise*, not do trip planning.