obscure grammar rule?

[nico]

Hi

I've read the following sentence in a FCE practice book (tapescript):

"It's a number of years now, Lionel, since you brought out your illustrated book on garden plants."

Shouldn't it be "It's been a number of years..." or is there some obscure grammar rule that I'm oblivious of?

Looking forward to your comments

Nico

[Anglika]

It is a fairly common example of a normal spoken structure.

The sentence could be said as either "It is a number of years" or "It has been a number of years", but the first is what I would expect in an interview of this kind.