As ems noted 'couple' can be regarded as a singular unit. Here are some examples: of 'couple was':
http://fraze.it/n_search.jsp?q="couple+was"&l=0&t=0&ffo=false&findid=-1&ff=
:lol: No way I'm taking the writings of modern "journalists" as fine examples of adult literacy. What a joke the majority of them are.
More importantly, you yourself instinctively interpreted this situation as plural. Furthermore:
“Are they a couple?” “No, they are just good friends.”
http://www.merriam-webster.com/dictionary/couple
Consider, if you will:
"There are two people left to see, but their needs are simple and shouldn't take long to deal with".
"There is one couple left, but their needs are simple and shouldn't take long to deal with".
"There are a few people left, but their needs...".
However:
There is a large crowd in the park and it looks like it has the whole area blocked off.
The first and third examples, I think we agree on; "people" removes any doubt about plurality.
I put it to you then, that when referring to the crowd, we conceptualize it as a large entity. We know it is made of people (plural), but when acting as a crowd, we perceive it as a single entity. We seem happy to use the singular forms here.
When we say "couple", at least in reference to two humans, we view them conceptual as two people who are connected to at least some extent. As I mentioned above, I think you see it this way too.
Honestly, looking at that 957 examples thing, one after the other I was ticking off, "Nope, plural. Nope, plural again. And again...".
I'm afraid I reject the singular, at least insofar as two people are concerned. I can't really think of an exception even.