Well, it can help, but then that also depends on whether it's even good. There are plenty of stories with irrelevant romance sub-plots serving to annoy rather than give any sort of bonus. Sometimes ppl demand for some romance, sometimes they wish it never even existed once the romance has been added; it depends on the story, and just how well two or more characters fit together. Some will also turn away from a story upon instant when they realise it must lack romance, though they can't be generalised as the majority.
And also, there are plenty of stories out there which are popular and lack any sort of romantic plot, like the ones the users above have stated. So no, it's most certainly not mandatory.
Think of it as the fries to a burger; whether the fries are there or not, people will still eat the burger as long as the burger seems or is tasty to them. Of course, some want the fries, but there are those who won't even bother eating them, and consider it more of a waste. Some will just eat them regardless, not because they want it, but just because. Now, take your story as the burger, if it's interesting (tasty), then it's interesting, regardless of the lack of fries (romance), and people will still read it (eat it).
That might not be a good comparison, but oh well, this is what I think.