I don't think the defense of any individual vague rule comes from a desire for vague rules. Even when going rules light, rules should be clear, concise, and work as intended, though it's okay if they require some adjudication.
The defense of a vague rule happens as a defense against codification. The stronghold rule is a good example. The rule itself is poorly worded when you think about it. But the intent is clear. Thus the rule as it's written is defended because altering it at this point requires errata, which is obnoxious, and risks unnecessary codification.
There is also a clear desire among some for the rules to be left as they are, without errata, forever. For this to happen, it must be left to individual DMs to clarify any unclear or poorly written rules.
Personally, I think it's exactly the kind of rule that deserves errata, because clarifying the language to match the obvious intent simply helps people who buy the newer printings. But I understand not wanting to open the flood gates on errata.