I recently got married and didn't have too much trouble with RSVPs, so don't stress too much - I think the more formal the event the more likely people are to realise the importance of hte RSVP. A casual party is more at risk.
The story tells us "the survey found email, text messaging or telling the host in person were the next most popular RSVP methods" and I think that is very important to bear in mind. While I do it, I hate with an absolute passion calling to RSVP. Especially if its a stranger (like for a shower or whatever, where maybe I don't know the host). I just really am uncomfortable making phone calls - I hardly call my family or even my best friend!
I think the easier you make it to RSVP the more responses you will get. For example once in a while a couple will include RSVP cards & envelopes but not pre-postage them. Well... they are kinda asking for it IMO. Not entirely - a guest should still take it on themselves to RSVP - but the host is ensuring at least some people won't have stamps, won't notice, won't remember, etc.