Are virgin holidays allowed to display personal details about me?

I received a letter yesterday which had my name, address and date of birth clearly visible through the viewing pane on the envelope. I know the postman needs a name and address to deliver a letter, but he certainly doesn't need my date of birth. In the current climate of identification theft etc. it's annoyed me that virgin have now displayed my date of birth to anyone that's seen the envelope. What would you do? Am i just being too petty about this or should i seek some kind of apology off them?