If you even remotely suspect something is wrong, you owe your child a speech evaluation. You can probably set this up through your school district or a therapeutic preschool. Our pediatrician did not seem to take me seriously when I suspected a speech delay, and there was one. In fact, we found out our son has autism. We have had the blessing of wonderful therapies and interventions, and now he is thriving. If nothing else, you will have peace of mind if there is no delay, and you seem to have no peace of mind wondering about it. Please look into it, for both of your sakes.
If your child understands what is being said when spoken to him I wouldn't be overly concerned. My Brother's youngest daughter did not speak until she was almost 3 and a half years old. She would say basic words to get your attention but then she preferred to point to what she wanted. All of a sudden she just started talking in complete sentences, which totally surprised the majority of the family, and has not quit talking since. She is in the 8th grade now and very smart. She is somewhat shy but is coming out of it. Be patient but consistent in expressing that you want your child to verbalize his needs and wants. I wouldn't be surprised if he doesn't all of a sudden surprise you with a complete vocabulary.
I understand your concern because I was in your shoes a few months ago as well. My son is now 26 months and before he turned 2 his vocab was only of 15 words which should have been 40 or something. Right around his 2nd b-day I made an appointment to see a speech pathologist. We got the appointment only when he was already 25 months. Well from 24 to 25 months in that 1 months spam his vocab boosted. His vocab now is in the 100s. He is still a little delayed in speech because he is not yet putting sentenses but they will tell you as long as you see improvment weekly or what not then he is fine. Boys also start much later then girls plus every kid grows and developes at their own rate. I've learned to accept that. Although my Son does not yet fully talk, he knows abc, 1-5, 5 shapes, 5 colors and much more. I think your son will be just fine. Dont worry
He is not even two yet--let him be a little longer. I am sure when he is ready he will talk to you. Also, does he have a history of ear infections? I am only asking because that may delay a little ones speech--but as long as he is starting to talk and understands what is being said to him you are fine--my little guy is 30 months old and there are still times I can not understand what he is saying because it is a newer word so just trying to get the pronounciation down.
If all else is normal with your son, you needn't worry too much about this matter. He is a bit delayed in his speech developement, but he is responding to directions (receptive language) and he is learning new words (expressive language). Most children are not at the precise same stage of development in all areas, and this appears to be the area in which your son is lacking a bit. You'll likely see an increase in the rate at which he picks up new words.