There are many reasons why men may find 'not-entirely-natural' women more attractive.
One reason, perhaps obvious, is simply based on evolutionary preferences. A rosy complexion may indicate good health, whereas larger breasts may signify fertility. Whether fake or not, women use makeup and surgery to accentuate features that men already find attractive. Though it is true that some women may accentuate features to the point of unrealism, it is worth noting that aesthetic reactions are established prior to one's cognitive appraisal for attractiveness . The mechanism in our brain that judges instantaneous beauty is likely not privy to information such as 'that woman in front of me has fake breasts'.
That being said, I think a better answer to your question relies on the notion of fluency--the metacognitive experience of difficulty associated with any cognitive act. Familiarity fosters high fluency, because our mind processes familiar things more quickly or easily than novel things. Several studies have shown that familiarity or fluency leads to an increased rating on any number of positively valence dimensions, including likability and attractiveness.  (As a side note, it's also interesting that the reverse is also true-- attractive faces are judged a more familiar ).
The media certainly plays a large part in increasing this familiarity through what we see on TV and in magazines. Different cultures develop different cultural norms for attractiveness as a result of their exposure. The same effect is frequently observed in people who are attracted to others of the same race. This preference is shown even in young infants, as a result of increased exposure to faces of their own race. 
Lastly, the 'message' conveyed by media likely influences our perception of beauty as well. Ads tell us that we have to constantly use the right shampoo, or diet supplement, or facial cleanser-- pressuring us to believe we won't be beautiful if we don't use these products. The message is not cryptic-- products often reference the 'healthy' or 'attractive' effects of their use. Perhaps someone better versed in the literature on belief formation or persuasion could add some useful citation here as well, this it not my area of expertise. (I often refer people to Cialdini's Influence: Science and Practice for an overview of the literature related to persuasion, which may be worth checking out if no one can provide more targeted references).
 Peskin, M. & Newell, F. N. (2004). Familiarity breeds attraction:
Effects of exposure on the attractiveness of typical and distinctive
faces. Perception, 33, 147-157.
 Reber, R., Schwarz, N., & Winkielman, P. (2004). Processing
fluency and aesthetic pleasure: Is beauty in the perceiver's
processing experience? Personality and Social Psychology, 8, 364-382.
 Monin, B. (2003). The warm glow heuristic: When liking leads to
familiarity. Journal of Personality and Social Psychology, 85,
 Kelly, D.J. et al. (2005). Three-month-old, but not newborns,
prefer own-race faces. Dev Sci, 8, F31-F36.