The bottom line really is that no-one actually "needs" bushes to turn a pen. Yes it can be easier but it can also lead a beginner to undersize the blank by turning down to the bushes and not allowing for sanding, it's also true that it's easy to catch them with a tool and sanding can reduce the size of the bushes as well as the dust discolouring the blank.
If you want bushes but don't want to pay for them it's quick and easy to knock some up out of deralin, perspex, corian or even offcuts of acrylic blanks, no need for tubes just drill out the same dia as your mandrel and while about it turn a few cones to use when sanding and polishing.
I have several sets of bushes I bought in the early days but wouldn't do it now unless I needed to set up a production run and short of time. It's nearly as quick to turn between centres using calipers.
In real terms anyway if you buy bushes for £4 0r £5 and get 20 or 30 pens out of it then IMO that's not extortionate. I doubt Phil or Dan are going to get rich selling bushes! 
BTW I can't agree with the wheel size argument Paul, I recently changed my car, a 6 week old demo with 20" wheels but it could just as easily have come with 18" or 19". Yes the characteristics would be slightly different with an identical suspension set up but so would it be with different tyres. Mine has all season but tyres from different manufacturers all all different and are much more important to handling than wheel size. However as you said it's a poor analogy.
