Pete and I were wondering when someone would spot this.
Its a mistake, pure and simple. However its not a mistake in the way you're framing it Gran, but a mistake with how Strike Rank should be calculated.
In playtest SR was calculated as described in the Adventurer chapter, based on SIZ, DEX and INT. However there are problems with doing it this way; for instance, how could SIZ realistically influence SR for missile weapons? We tested SR both with and without SIZ and the concensus from playtesters was that it should be based on just INT and DEX for all characters and creatures - which is exactly how it is presented in the Creatures chapter and which you've noted.
The Adventurer chapter is wrong. I did correct this before the book went to press but somehow it slipped through the net. Its one of the first entries in the Conversion and Errata document which I've just submitted for production.
I think though, that the point you raise about large creatures having some form of SIZ advantage is valid to an extentt; but you do need to remember a couple of things. SR is essentially about
speed of reaction. SIZ is also not a guarantee of speed (and often the opposite is true). Reach and weapon size is taken into account with the Reach and Size entries for creatures' natural weapons. Thus, leaving SIZ out of the equation for all is the best way to handle things.
Unfortunately, the change into the Adventurer chapter went awry somehow - although the correct SRs are in the Creatures chapter.
We do apologise wholeheartedly for this error. It should have been spotted but somehow slipped through the net despite a
large number of eyes going through the proofed layout document.