I just picked up a fairly new Squier and the neck is certainly a wee bit wider than my Fenders. I think that with any neck replacement there is always a chance that a bit of adjustment will be needed.
55.5 mm wide I think is the 'standard' but I measured a bunch of various Fenders, Squiers and after market necks and neck cavaties recently and there was a fair bit of difference between them - just a fraction of a mm here and there but enough to need a bit of modification.