speech therapy

am a bit concerned that my otherwise perfectly healthy and happy 20-month-old Son might be way behind in his speech.  He says only 3-4 words right now (Hi, bye, bye) but not much else.  She sometimes babbles in "goo-goo language with animated and interaction behavior and tones, but does not form any coherent sentences.  He knows what objects are; for instance, if we say give me Elmo, she will do so correctly.  Rather than say yes, most of the time he will bounce excitedly if asked an affirmative question.  He doesn't say no, but will put his hand  up if he doesn't like something. He will often screetch aloud in delight, and exhibits an attention-getting yell when he wants out of his crib or high chair.  He loves to watch television and gets noticeably excited when his favorite programs come on, oftentimes singing along with the Wonder Pets or tries to mimick the words that are asked to be said wehn watching Go! Diego! Go!  He is very affectionate and has learned how to give kisses and hugs when asked or sometimes he will voluntarily walk up to me or his dad and give us hugs and kisses.  He has started to use pens and markers, and his fingers show dexterity (grabbing small objects, typing on a keyboard with his fingers).  He peruses through books and photo albums and will turn the pages often babbling as if he is reading.
He constantly carries objects around and can toss a ball. He attends nursery school and I was asked by one of his teachers if I would like him to start Speech Therapy because he is not intelligbly verbal at his age. I declined the offer and am wonderng if I was hasty in my decision considering the fact that he does not say as many words as he should be for his age.  I have been reading some online articles about oral motor skills and it speaks of chewing food and strengthing muscles in the mouth. I did need to add that he is a big eater and when eating he only takes 3 chews of his food -meat in particular- before he swallows.  I feel that he should be chewing it more.  I try to get him to chew more to no avail. Could this behavior being inhibiting the strengthing of the oral muscles needed to form the correct structure and tongue placement to or consonant formation? Is it too soon to be discussing Speech Therapy?

Any advise on this matter would be appreciated.

[mammo]

I say "let him be."  He is doing so well in every way, and many are slower to talk. In my grandson's Daycare they taught the ones who were slow to talk sign language, and my grandson was one of them.  He has just turned 3 and talks up a storm.  Every child is different and they understand a lot more words than they can actually say.  You can work with him by asking him to say "toy" before giving it to him, "cookie" etc., but this didn't work with my son who was slow to talk nor with my grandson.  One day he will just start using more words, almost overnight.  Relax, he's fine.