I think there's a combo of things - these are definitely women who have won the genetic lottery and would look amazing anyway. Totally jealous.
However, there is a very, very wide spectrum of 'work' - from incredibly expensive high end products and treatments, to lasers and hair extensions and teeny tiny bits of surgery (you can even have eg laser 'tightening' of skin e.g. Under chin and a laser freezing of fat cells around jowls that freezes them and kills them 
). There is a cosmetic dentist in NY who will give you a rejuvenating teeth treatment for $100,000 - ordinary mortals don't consciously notice that our teeth and our smile 'age' us, but they do. The treatment is quite complex (for $100k it'd need to be) but it's all about subtle gum treatments, whitenings, reshapings, veneers if necessary, bits of filler - not at all like the bright white cheesy smile, designed so you would just think 'what a lovely smile so and so has'.
I have several friends working v deep in celeb land and it's phenomenally naive to think that women earning multiple millions of dollars in an industry that values them primarily for their looks wouldn't invest tens of thousands of dollars in that appearance. It's not a judgement - I think they're doing the right thing.
When I got married I had been working like a maniac in a corporate setting and being quite tough on myself. I decided to go all out on my appearance for once - Pilates every day, tons of Tracy Anderson work outs (trainer to the stars, REALLY hard and sooo boring but v effective) ipl to treat some acne scarring and rosacea, balayage from most expensive salon in London, makeup lessons (had to do own wedding makeup). I looked SO much better than i normally do, but it was sooooo expensive to maintain and so much work - since I have a day job and two kids now I could never look like that, I don't have the money and discipline and commitment. There was a VS model on fashion police yesterday and the panel were all 'HOW do you maintain your figure' and she replied 'I go the gym seven days a week and workout for hours'. Gwyneth and Kim K who are at least quite open have both admitted to fraxel (quite jealous of that). So obviously these are stunning women who got into the industry at least significantly because of their looks (there are millions of amazing actresses who didn't make it because they're not deemed pretty enough) but who then invest in keeping their looks as great as possible by lavishing money on it and treating it like a job.