When I picked up my bike from Spa it had a stack of spacers on top of the stem. The guy said "I've left a few spacers on ..." and gave me a menacing look "... for when your back goes".
In the years since buying it I've fiddled around and moved the bars up and they are all underneath now.
If they hadn't left me a conning tower of spacers and had cut the steerer exactly at the height we decided on when I test rode and ordered the bike I wouldn't have had the opportunity to move the bars up.
It comes from the finality of the act of cutting the steerer to height. Best to leave a bit extra on, even if it does look a bit funny. Also enhances the resale value of the bike as it's more adjustable.
Some super aero bikes have integrated seat posts that are cut to height so saddle height adjustment is limited. We had a thread on here recently from someone who had bought one second hand and was having problems.
sorry misunderstood you - i was thinking of the stack of spacers Thorn seems to like to leave below, when I would just go for a bigger frame - but that's a separate issue of course.
On keeping the steerer with the conning tower until your back goes, is there a risk of impaling yourself on the thing?
I have two ahead bikes - both essentially cut - and several threaded headset bikes/builds - will admittedly probably have to buy new stems with latter as Ridgeback in their wisdom supplied short stem columns (or whatever they are called) as standard.
An adjustable stem would have sorted your back issues if the steerer had been cut?
I know some folk object to them - I don't.
German outlets tend to have a good range - but problematical these days of course.