No, not all cultures have a flood story, Theland, a lot of them do, but not all.
Most people accept that the reason these stories exist is twofold:
1) Cultures nick from each other (your own religion being an excellent example of one that co-opts other people's stories).
2) Localised floods which have a catastrophic effect in that region. No one would deny ancient localised flooding in the Middle East.
As for the water coming from below the tectonic plates, there are a number of problems with this. The first is that it's utter rubbish. There is no water beneath the tectonic plates and never has been. End of argument.
But hang on, let's assume you're correct. So, you've magically invented a load of water that is capable of covering every land mass in the world. Now all you have to do is explain how Noah, family and animals managed to survive the increase in humidity. (And of course, you have to explain how he managed to get so many animals and food stuffs into a vessel of 1,518,750 cubic feet, not to mention explain how the crew could cope with the daily volume of excrement produced).
Of course, you *can* attempt to argue that God changes the rules of physics and chemistry as he pleases and threfore the water could come from beneath the plates 'ner ner ne ner ner', but then you're back to a defence based on pure faith in the Bible. As we know - and you're yet to refute - the Bible is provably wrong, therefore your faith in it seems peculiar.