mjd - you appear to be under a misapprehension about highway=trunk/primary. When you say

I always thought "trunk roads" connected major areas of industry/commerce/population.

Indeed. More formally, this network connecting major areas of industry/commerce/population is called the Primary Route Network, and is signed in green on the ground. The roads are of no particular quality, so you get some dual carriageways, some roads built to motorway standards, but also some pretty bad roads which nontheless are the best road linking their major areas.

I can't comment on whether the roads in your area form part of the Primary Route Network as I've not been there. But if they have green signs, they should be highway=trunk; if they have white signs, they should be highway=primary. It's quite possible, however, they have white signs, in which case this alteration was wrong.

In the UK you might be tempted to interpret 'trunk' differently, meaning a centrally-maintained road (as you seem to be by saying the government is removing them). This would be wrong for our purposes. Having Highways Agency-maintained roads showing as green and county council-maintained-roads will be useless for navigation - as roads are officially 'detrunked' they are not downgraded in quality; having the colour depend upon the organisation paying the bills for maintenance is not going to be terribly useful.

I'm unsatisfied with the use of two differing interpretations of what highway=trunk/primary means in the United Kingdom on the map. Tagging the Primary Route Network is consistent with other mapping providers, easily shows the routes recommended by the government for getting between major destinations. Tagging the roads funded by the Highways Agency is of no use to anyone that I can tell. Can we all agree on this please?