Monolingual biases

I have often come across the assumption that bilingual children are slightly slower than monolingual children in acquiring language (whatever that actually means, i.e. are they later at speaking, but equally good at comprehension, or is there a delay in both?) In any case, our doctor said this to me when we brought our son in for check-up at 1 year old and asked whether he was producing any words yet (he wasn't!). We were told not to worry, bilingual kids often started speaking later but then quickly catch up with their peers. I have heard this also from friends, from other parents, from babysitters and nursery staff. I think I actually kind of believed this to be true as well, maybe because my son started speaking words slightly later than my friends' children. But then I thought, actually most of my friends' children are bilingual too, so why am I assuming that my son is slower because he is bilingual??
Surely we aren't dealing with any kind of "delay" caused by bilingualism, but just experiencing first hand the common variations found in speech development, just like there is variation in the rate of motor skill development, i.e. differences in the age a baby first rolls over, and first sits upright. (Not that it's a race, but my son was very fast with this stuff :) (Incidentally there seems to be another assumption that your baby will either be verbal or physically active...which is probably another myth).
Anyway, so I have looked into this a bit and in fact it seems that indeed there is no evidence to suggest that bilinguals have any kind of delay in lexical acquisition (i.e. learning words!). The perception that a bilingual child knows less words than a monolingual child comes from the simple fact that most observations are made in only one of the child's languages. If you observe my son at nursery (in an English setting, the language that he is receiving the least input in), he will most likely not say much at all! (I would actually love to be a fly on the wall and observe him at nursery, because I really don't know how much English he knows!)
A bilingual child may appear to know fewer words than a monolingual peer in one of their languages only. But if you look at both languages, no difference in word acquisition rates has been found. In fact, some studies suggest that bilinguals may actually have slightly higher word acquisition rates than monolinguals.
So yet again this shows that we have monolingual biases in our approach to bilingual children, and that it is never enough to consider just one of the child's languages or language settings in order to get an idea of how well he or she is doing.
As I mentioned in my last post, there are more bilinguals in the world than monolinguals, so by sheer majority, shouldn't we re-adress this bias, and study the effects of monolingualism on development, not the other way round?