First of all, he's being dick. To continually remark on the attractiveness of attributes your partner doesn't have is insensitive and cruel, but to say that resulting unhappiness is their fault for being insecure is awful.
Saying that there are many, fairly common explanations for his attitudes. Sometimes men develop an idea that the women they find attractive should be notably shorter than them. It can appear that men in relationships with notably shorter women seem more masculine. It's just one way in which ideas of sex and gender can get a bit twisted. He might even have only just realised that shorter women are attractive and thus be going through a phase, having previously associated attractiveness with taller women, as was previously the ideal within Western culture.
It's not unusual for men to not find some supermodels attractive. They end up as supermodels not by being universally attractive to men, but by fitting a certain aesthetic. It's not the case that all tall women look alike, or indeed women of any height. My girlfriend is 5ft 7, but that doesn't mean I find all female film stars of that height particularly attractive.
I hate to say this, but it might be worth considering whether porn is a factor. In recent years, mainstream porn has come to increasingly fetishise smaller women. Abstaining from watching porn, or a least porn of a certain type, can de-fetishise the libido.
Holding certain ideas doesn't necessarily mean that he can't drastically improve. For all I know he might be really nice except for this one aspect. I myself used to, on occasion, say awful things to my girlfriend. But her telling me that she couldn't put up with it forced me to change, so much that she now (two years later) sees me as the more considerate partner.
Essentially, he could be saying this for many different reasons, but if he won't stop being a dick to be with you, then he probably isn't worth being with. He really shouldn't be saying that kind of thing.