If the milk marketing budget is truly 100 million a year (a cursory check shows it's likely closer to 200 million now) as he mentions, 10 million doesn't seem very high at all.
So they've had a 100 million per year marketing budget for at least 10 years. Let's say they spent 1% per year towards the domain... The opportunity cost for not having something as obvious and useful as milk.com seems significant. To me it seems like they've already made a mistake by not paying up despite having the means, and now they've dug their foot in. They've spent hundreds of millions on billboards, yet they can't even put "milk.com" on their billboards next to "got milk". Imo but 5% less billboards for a few years and buy the domain...