Yes, you're right, the distinction has become largely meaningless, with or without the tunnel. But the British still often find it irresistible to refer to the 'continent', at least the BBC and some people I have met. The term irritates me, a you-and-me distinction of exclusiveness. There are conceivable circumstances when mainland Europe might be affected and not the Britain and Ireland, for instance animal or plant disease, climate, etc. So the distinction cannot be entirely rejected.