PhotoStream on iPhoto-MacBook is different from PhotoStream-iPad I see so many pictures that I have took with iPhone on iPad Photo Stream.
But today I also wanted to activate PhotoStream on iPhoto on MacBook. So did I ! but the images it has downloaded are just around 20 photos, there are so much more if I go to PhotoStream on iPad or iPhone but on PhotoStream on MacBook there is just a few of them.

Shouldn't they all show the same thing?
Apple has a fairly comprehensive troubleshooting article for isolating any inconsistencies like you have observed and clearly, the design of Photo Stream is that there is one set of pictures available from the cloud (the web  interface) as well as each device that has the stream enabled.


TS3989 - iCloud: Photo Stream troubleshooting


Why not work your way through that document and then ask a second question if needed if you run into problems on a specific step? I like to power off both the devices and then start with one to work through the process to see if it's working properly, and then proceed to the next device or computer.