This specific rule does not apply to the dependents (spouses) of British Citizens, or those settled, however does apply to the dependents of those who are resident here under the Points Based System (pbs), such as Highly skilled migrants.
This creates "one rule" for them, and "one rule" for us, effectively having a human rights provision (overriding R320) in the case of those married to a Brit, but not those married to an American living here under Tier 1.
It is (of course) entirely posible that Rule 320 is in it's current form in breach of the RRA.
The other major problem with Rule 320 is that it is summary justice handled administratively. Once a Rule 320 barring decision has been made by an Entry clearance officer, all further applications will be automatically refused. They then have to be appealed, which will normally take upto 8 months to have a hearing date.
At the Hearing, the appellant will not be able to attend, as the hearing will be heard in the UK, and they will be overseas and not given entry clearance (thanks to the Rule 320) to come to the UK to attend the hearing.
This is rather unjust to say the least.
Rule 320 could be made to be fair, if say the UKBA had to apply to the Tribunal (affirmatively) for a Rule 320 "prohibition order", against the person, and demonstrate to the Tribunal that the person had breached the rules, and thus an order ought be made against them (at which point the person could employ someone to defend them (although it still should be pointed out that they would not be present)), but in it's current state, it is a blunt tool, of the worst kind of administrative penalty.