Not every one needs or wants specifics. Not every one is capable of communicating at the same level so expecting that from everyone is unreasonable. Not all situations call for detail.
Also vague compliments can be a person's way of putting their foot in the door for more conversation, which could lead to the specifics later, when it is known that it is welcome and the feelings are mutual.
If its a new acquaintance, being too specific can feel creepy. I've found myself thinking things like, "how long has this guy been watching me?" and "he's thought way more about this/me than is reasonable."
Now, if you go deeper into getting to know each other, specifics should come up. However, in the first few conversations, too much detail can feel too personal. For me anyway.