CSS and HTML will usually afford a specific approach. Being a web developer is knowing what these approaches are, and to know when stuff might get "not nice". So when you see a graphic designer using multiline text blocks with elided text in their design layouts, you know to raise a red flag and get that removed.

Personally, I've not found collapsing margins a huge issue either way. It's just the way it is. There's 10 billion ways to add distance between two elements in the browser, so pick a solution and go with it.