It doesn't matter if you utilised them on this occasion, presumably you'd want them to be available if your dog did suddenly need them, so the practice has to buy them, then pay out regular costs involved in maintaining them. It's about the baseline cost of running the practice, rather than costing out what happens at each individual appointment, which would be impossible to do.
The practice needs to charge out it's appointment slots according to how much it takes to run the practice, plus some profit on top. They are not charities, they are businesses and as Lonecat and other vets have said on this thread they have extremely expensive running costs, plus professional development etc to pay for, before they even start paying themselves.
GP surgeries don't have the same overheads, hospitals do, therefore if you go to a private hospital appointment, even for basic treatment you'll find the charges are higher than they would be at a private GP, for the same reason - overheads.
Yes, you would have had to pay more for an xray, because that would involve the cost of actually using the machine and paying someone with the training and expertise to operate it, plus someone with the professional skills to analyse the results. The basic consultation charge, would include the vet's time and professional skills, heat, light, nurse and receptionist wages and a proportion of the cost of running the practice that comes/came from capital expenditure on large items of highly expensive equipment. If your dog ended up in theatre there are then the costs involved in running the equipment, which are additional to the cost of buying it in the first place.
Don't get me wrong, I still take a sharp intake of breath every time I have to pay a vet bill, because they aren't cheap, but I understand what I am paying for and accept it as a necessary part of pet ownership. I paid out over £5,000 in vet bills last year - at a time when my dogs' insurance had lapsed (entirely my fault). I could really have done without spending that money, but at the same time don't begrudge a penny of it, it was necessary for the health and wellbeing of my dogs. Needless to say both my current dogs are now fully insured again.
Last year I came on here bemoaning what I considered the ridiculous cost of organising a pet passport for my dogs. I now understand that, while I thought it was just a quick jab and stamp/signature in the passport booklet, it actually involves extra training and registration, which I believe has to be kept up to date, for the vet (so extra costs incurred there) plus a mound of paperwork that has to be filled in accurately and sent to the ministry (can be up to an hour in addition to the actual consultation time). In addition many vets have to take out extra insurance against potential issues re pet passports and travel abroad as it's a massive area of litigation at the moment and one slip in the paperwork can land them in a whole heap of trouble. I had no idea, but now understand why they cost what they do.
I often find it's the drugs that cost the most when my dogs are ill, however in many cases you will find the vet is willing to give you a prescription to buy them cheaper online if you ask, as they don't make all that much profit from them.