Pair of Docs Paradox?
In a story called Dogs Of Doom, in the December 1984 Marvel Doctor Who Comic, Vol. 1, No. 3, the 4th Doctor remarks to Sharon, "It's high time the Tardis had its ten thousand year service." At the 4 minute mark of the televised episode Time And The Rani, the 7th Doctor comments that he has to book in a bicentennial refit of the Tardis.
At first glance these two facts of fiction could seem paradoxical. You'll give yourself a headache if you over-think it, so don't, because there's room for both truths in the Whoniverse.
A 10,000 year service of the Tardis has nothing to do with the age of the Tardis, rather it is the amount of time through which (via the space time vortex) the Tardis has traveled, whereas a bicentennial refit would include maintenance or repair of those bits and systems which need replacing or servicing over the course of time, not time travelled.
Unlike an automobile, which transports its occupants from one place to another in a linear sense over distances in units of measurement we call miles, the Tardis traverses time, space, or time and space, but not in a linear sense for it dematerializes at the point of departure and then materializes at the point of destination. It did so at the conclusion of "An Unearthly Child" when it traveled back in time, but not in space, to the point in history contemporaneous with "The Cave Of Skulls."
An automobile travels in the present and only in the present. In a physical sense the Tardis can travel the same way as an automobile, from Point A to Point B, but it can also travel in time, so it would make sense that service intervals for a Tardis would be measured in years, not miles.
Personally I'd like to see more on screen Tardis maintenance. The new series has from time to time given us peeks at the inner workings of this fantastic machine and once every so often we see the Doctor and even a companion involved in repairs and maintenance. The amount of maintenance a typical earthbound auto requires is not insignificant. Something as complicated and sophisticated as a Tardis would seem to give new meaning to the phrase "high maintenance"... so why not make it part of the lore?