The track line in a Boeing is just as much influenced by IRS drift as the similar displays in an Airbus.
- I think you'll find that in the Boeing 'Track' is computed from the FMC position, ie normally DME/DME or GPS? In any case, you've either got an INCREDIBLY powerful VOR or LOC if you can get ANY noticeable IRS drift in the time span available (or a crappy IRS...................
).
EDIT: ACTUALLY I'm not sure about Boeing's 'Track', but I have NEVER seen IRS drift of the magnitude you are suggesting on a 737!)
The 'Classic' 737 suffered from an 'out-of-date' FMC mag variation database which would give you 'drift' in still air while tracking a radial and 'offset' the localiser a degree or 3 plus change the runway QDM for you.