There are two points to make here:
1. The lack of real time information -
Because the routeing and safety margins of trains are determined by someone/something external to the train itself (i.e., the signaller) robust methods of determining and communicating the location of every train (to within the appropriate safety margin) have necessarily been developed. A nice by-product of this is the ability for the signalling system to impart this information to the customers using information screens. However, the real-time information feeds we get are merely a convenient byproduct, which is also why they work so badly in times of significant disruption (the information screens only know a subset of the information that the signallers know).
For a coach or bus, fundamentally, for routeing and safety purposes, the only person that needs to know where the bus is is the driver. Any real time system would be a significant, and fundamentally unneccessary, addition to the existing infrastructure in place to support the coaches.
Since the coach companies are operating in a substantially unregulated market, all they do, and all they can care about is their bottom line. NX, Megabus, et al. exist to make a profit, and that alone. Any other behaviour (transporting passengers) is a byproduct of their main purpose, making money. Now, there are some customer service aspects which will help them make more money, so they will do this, even if it costs them in overheads in the short term. Real time information is apparently not one of those things that they believe their customer base cares about enough to make the difference between buying that coach ticket and not buying it.
2. Timetables.
As has been said above, Coach timetables are available in all of the Traveline databases. If you want a PDF timetable, may I suggest going here:
http://www.travelinesoutheast.org.uk/se/XSLT_SELTT_REQUEST?language=en
and typing in the route number or destination