Why call all these things cupboards?

I find the English language is kind of like Buffy canon: there are some things you just have to fanwank, because they make no actual sense whatsoever. :-) Better question: why is it spelled "cupboard" but pronounced "cubburd"?

we just call them bathrooms

Which is a euphemism I never understood. Why not simply call it a toilet? Why call it a bathroom if there's no actual bathtub in it?