Yep, I agree with that too. I think some breeds are more interested in having a playmate as well, collies for instance tend to be very people orientated dogs, but labs love to have another dog to play with!
I think two things to consider before getting a second dog are
1) is my current dog at a stage where I am happy with his training/behaviour etc?
The reason for this is a new puppy will most likely copy the older dog, if your dog has a habit you seriously dislike then its best to fix that before introducing a puppy which is liable to pick up the habit (they always seem to mimic the bad habits!). It is also said that dogs can revert backwards when a puppy comes to the house and may even 'lose' some of the training they previously knew.
2) is my dog ready for a companion?
That is a simpler question, some dogs mature faster than others. Some dogs when young would be too rough for a younger puppy, some need a bit of time to 'grow up' mentally. There could be other things too, like a nervous dog may need time to grow in confidence, or a dog with socialisation issues may need this worked on first.
Finally, a person needs to decide on the 'age gap' they prefer, and this is very much a personal choice. I have made the decision to wait until Cadbury is about 3, as this gives a nice gap and means when he is old the other dog won't be. Despite this, at times I think it would be nice to have a pup sooner as I can see Cadbury losing some of his 'puppyness' and he isn't so mad keen to play the silly pup games. Having two pupsters together is very tempting
And then of course even when you have made the decision you might have to wait quite a while before the ideal pup comes your way.
Each to his own, I say.