The Daily mail headline was crass because it was crass - because it reduced the lead story of the day to an adolescent guffaw at a silly word play and to the shoes and legs of the women in the photo, not the important constitutional issues which they were discussing.
As far as what they were wearing being worthy of comment - sure. An inside column noting their respective styles and body language would have been worthwhile, but that's not the lead story, nor should it be the front page headline, still less expressed in such a sophomoric way.
On the side of the Daily Mail, it is worth noting the vast number of column inches the self-righteous writers of Guardian devoted to Theresa May's leather trousers not too many weeks ago, and their disapproving coverage of her recent appearance in American Vogue magazine. I suppose the Guardian writers believe it is all right when they do it because they are, after all, the Guardian and so by definition it would be impossible for them to do anything sexist or non-PC.
I would also add that for all the umbrage expressed by certain female columnists and politicians, and the idea that men would never be subjected to that kind of personal scrutiny - men are subjected to it too. There is just much less of a hoo-ha by the 'victims' when it happens. President Obama, for example, was castigated last year for having the temerity to wear a brown suit, instead of black or navy blue. David Cameron's hair, and Boris Johnson's too, regularly receive comment.
In terms of worthy commentary, I would say Theresa May is to be commended for her dress sense - she is happy to push the boundaries of what is considered 'susceptible' for women in their 60s by wearing thigh boots and leather trousers as and when she feels like it. And she manages to carry off the look. That speaks of self confidence, strength of character and a willingness not to blindly follow the herd - good attributes in a politician or a person and worthy of comment.