We know this is just a fraction of what goes on (and training is necessary) but the taxpayer has to be convinced that it is the correct way to do things and more resources are needed. On an earlier thread there was comment about the troops not having the right equipment in Iraq, it may be the ultimate fault of the politicians but Joe public sees this as a failure of the services or at the very least a whinging service trying to blame the politicians for it's failures.
My guess is that if the public had a greater awareness of these things, as discussed here (and elsewhere) then their would be more approval for defence spending.
As an aside, from personal experience I know that the forces have to account for EVERY pound they spend, yet other agencies and organisations of HM Government are not so tightly watched over. An at the same time as demanding the Services do more with less people and less equipment, Mr Brown from No 11 is happy to give BILLIONS every year to the EU, and organisation so corrupt that its own accountants have refused to sign the accounts.