Breadmaster is right; St Patrick's day, as celebrated these days, is largely an American invention. Americans would do well to realise that on this side of the pond we merely like the Irish, but don't worship them.
Just to shove my oar in for a moment... British food and drink outlets seem to go loopy every St Patrick's Day, and I must concur with Rosie and Breadmaster's opinion that it's the US influence that fuels this. On the other side of the coin, I went into my local Tesco outlet (and it's the major one for the area) at the end of February to see what I could get to celebrate St David's Day (what with having Welsh ancestry). I was laughed at by staff. When I suggested that, surely, the massive efforts poured into their St Patrick's Day marketing might indicate a degree of 'racial bias' (I stopped short of institutional racism!), I was told "Well, you can buy a daffodil or a leek." I would have replied, but the manager had lost interest and walked away.