Actually, these backtracking events on taxiways happen quite frequently on airlines these days, particularly the low-cost carriers. The "Frequent Flier Miles" programs that have become so popular in the last couple decades are actually based on the accounting done for flight crews. Flight crews are paid per 100 miles per leg. It happens sometimes that an aircraft lands a couple miles short of a 100-mile increment on the sector. To roll-over, the captain will often take the "scenic route" to the stand/gate. Often this takes the form of an extra orbit around the terminal in ORD, or some claptrap about "the hispeeds" being "closed for maintenance" at PRG (exactly 697 miles from LHR, hence the proclivity for london flights to taxi all the way down the inactive before coming around to the terminal), or even the ubiquitous "our gate is in use".
When your flight does these things, it is customary for passengers to diminish the gratuity. I'd recommend giving the pilot no more than a fiver.