Well said crumpet and Ita with all of it.I also believe media saturation has altered peoples' sense of what is normal and of what is hot. If people are inundated with manufactured images of airbrushed people who look flawless, it becomes the norm to look at flawless faces and bodies. Reality becomes distorted over time, much in the same way that 24/7 media coverage of a few kidnappings makes us thing that kids are being abducted left and right and that it is happening with greater frequency when it actually isn't.
I think that media saturation promotes the idea that there is always something better out there. The fame obsessed culture promotes the idea that attention=power, even negative attention is better than being anonymous. The increased availability and acceptance of plastic surgery has gradually led many people to 'expect' that anyone with less than ideal features get them 'fixed' since science has provided the means to do so. We are more aware than ever in history of what is out there, thus we compare ourselves to others more than we ever have (this applies to consummerism in general). As we become more comfortable because our basic needs of food,clothing, and shelter are met we aspire to loftier and more shallow goals. Life seems to be about one-upmanship.
I agree that every culture and era has had its own beauty ideals, but in the past the ideals were more attainable and more tolerant of imperfections because most people didn't have their flaws erased by ps and technology didn't allow for all the airbrushing we see today. There are also more people so there is more competition for everything, including mates.
Let's not forget that the beauty industry relies on us feeling inadequate so that we continue to want their products and services. Thus, it is in their best interest to make the ideal as far from reality as possible so that people will continue to make them rich.