MJR - what's bizarre about having to track within 5 degrees? If you were doing it for real wouldn't you want to be on track?
5 degrees is the tolerance required for the IRT. Examiners have discretion and whereas you might stray outside the tolerance and pass, you can also stay within the tolerance and fail!
E.g. on a good day in perfect conditions if a candidate made no attempt whatsoever to correct a 5 degree error one might consider a fail. In other circumstances, weather/crew workload etc. a candidate might stray outside the tolerance but you would be happy to pass him. Essentially the examiner would have to ask himself whether he might have done the same thing in the circumstances.
Pilots sometimes refer to "limits" which is not the correct terminology - they are "tolerances" but essentially it all boils down to the same thing in the sense that the "professional" pilot is the one who is striving to fly the procedure accurately at all times.