I note an issue concerning the relevancy of Roman law has been raised.
Before I studied Roman law (and by Roman law I mean Roman civil law, not criminal or constitutional law) I had a very similar opinion to you. I felt I was being made to study an unnecessary subject due to an archaic tradition, and if I had been given the choice I would have been unlikely to have chosen the course. This view I discovered was wildly misconceived- I found that I greatly enjoyed the subject in its own right, but I also found that it is highly relevant. If I the course was not compulsory my interests in such matters would never have been spurred and I would be a different and probably more narrow minded lawyer.
The traditional reasons given for the study of Roman law is that it introduces you to the concepts of law- how different areas of law fit together. Students are taught land law, tort and contract in separate modules in their law degrees- Roman law shows you how these concepts fit together. A response to this would be that using another legal system such as English law would be equally appropriate, but given the wide area covered if one were to use English law for this it would be grossly oversimplified. Another of the traditional reasons for the study of Roman law is that it introduces you to another legal system and broadens your legal horizons. This too is true- but the cynics might respond why not use a modern legal system such as French law?
There is one overriding reason for the importance of Roman law- and it is one not often understood by people. I apologise for the gross oversimplifications here, time and space do not permit otherwise (I recommend Stein, Roman Law in European Legal History for a good introduction). Roman law was rediscovered and used albeit in a mutated form during the Middle Ages on the Continent as a (if not the- although this is controversial) legal system. It attracted a great degree of comment and its synthesis was applied as the learned law (again I apologise for the oversimplification). This in turn slowly mutated away from the original sources, before a wave of nationalisation of law occurred whereby a variety of states produced codified legal systems drawing of course upon the previously applied law- many synthesised Roman law. If one is to study say modern French contract doctrine, or the German law of obligations, knowledge of the sources is highly useful; and it helps to explain certainly similarities which are found across most legal systems. People who are focused solely on the English legal system will find that Roman law too influenced English law- particularly via institutional writers (I recommend Gordley, The Philosophical Origins of Modern Contract Doctrine).
Ancient learning can be useful and relevant- most courses on philosophy will cover the ancient writers in great depth, indeed one would be surprised if they did not. When one studies legal history- particularly legal history on the continent one realises that the Romans are to law what the Greeks are to philosophy. Knowledge of such matters will prove to be increasingly important given recent moves by the EU via funded projects investigating the harmonisation of various domestic legal doctrines such as contract.
Oxbridge are not the only institutions offering a course in Roman law- Bristol, and many of the Scottish Universities amongst others do likewise. Also if one wishes to see Roman law cited in the judgments of modern courts I recommend reading a few South African judgments.