I don't know what bikinis have to do with how a beer tastes, but they really make me want to go out and purchase some scantily-clad babes. Right away.
Luckily, i don't watch that much TV, or i'd get slapped more.
All kidding aside, advertising has largely transcended content. Especially with beer, they don't have to tell you what their product is, what it does, why you want it, what its side effects are; you know all these things. They mainly just aim to get your attention so they can have your eyes for a second.
So their main question is, who buys beer? Who buys beer in mass quantities, especially the cheap domestic kinds that bother advertising (since people that like the specialty kinds are likely to judge on taste and personal experience)? I bet if you had the demographics (and they surely do) you'd find that it's young men.
And they're not highbrow. You wanna fish, use a worm or shiny thing. You wanna rabbit, make carrot sounds. You wanna catch a fratboy - bare some skin, babe. Gotta move some product.