I think there are fewer upgrades now because the Boards are keen to resist as they have to declare how many adjustments were made and that doesn't reflect well on the original marking. Unless marks are judged outside of the correct band, even if considered rather generous or mean they won't be adjusted, as seen within tolerance.....and in some subjects, a level of limited tolerance in marking is necessary. Fewer changes to marks this year isn't an indication that original marking is more accurate....just tighter controls on what warrants a change to mark. I think marking is often very unreliable, and that's pretty scary, especially when you know that they hope to not adjust marks if a remark is requested. And if you don't get a change based on a re-mark there really is. I where to go with it, unless you can show maladministarion. I have known students given grades 2 below what their script was judged to be, when their experienced teacher who was also an examiner, judged it to be, when looking at a photocopy of their script, as a way to decide if to go for a re-Mark. So a remark was requested very confidently...but no change, and nowhere for the student or school to go with challenging it. Not a fair or reliable system unfortunately.
And yes it absolutely works better for those with the knowledge and funds to use the system. Some independent schools will ask anyone with a slightly disappointing grade or close to the boundaries to pay and request a copy of their script. Some will be getting 5 or more. Teachers then look carefully at the marking to see if it looks mean and if it does and they don't seem close to a lower boundary they advise a remark (pointing out the risk of a down grade too,mor course)...so then some parents are paying for 5 or more remarks. Of course you are more likely to get upgraded if you actually put in for it, than if you don't and lots of people don't, because they don't understand the options available or the timescales, or because there is no encouragement to do it by schools even when the mark seems highly surprising, or people simply don't want to pay or can't pay. In lots of Independnet schools, with staff and parents in the know, most parents will expect to be putting for at least 1 script back and remark.....there's no real serious consideration of if the higher grade feels deserved, simply a sense of you might as well try, and go for priority remarks which are more expensive as there's often a sense that earlier remarks are more likely to see upgrades than later ones, as examiners looking them over perhaps come under more pressure to hold the line.
And if you've paid £20k per year in school fees for many years, a couple of extra hundred is a drop in the ocean if there's a chance of an extra grade or two, and you're far from the lower boundary, so the risk is low.