I do not know how universal St Valentine is, but would have thought that it was more recognised than St Patrick.
On 14th of february they had snowikings, I did have a memory that they did have a Valentine uber previously but could find no reference to it on the forum.
As to the leprachaun they had it last year,but again why the big interest in only the patron saint of Ireland to the exclusion of all others?.
St Patrick is only really of relevance to the Irish, though they do make a meal of his day in the USA,as they tend to with anything they can co-opt to make money from, it wouldnt seem to make sense that another countrys game would introduce the concept, unless perhaps the programmers were mainly americans and they sold the idea to the previous owners of the game, or perhaps St Pat is also big news in Australia as well.
Except they did the turkey in November for thanksgiving and to the best of my knowledge, that is only an American holiday.