I, too don't like asking my dogs immune system to fight a whole different things at the same time and spacing out the vaccines makes sense to me.
There is an official "party line" on vaccines that doctors follow and there are alternative viewpoints some from no vaccines at all to some selecting and spacing vaccines and others giving all they can at every opportunity. People with opposing viewpoints span all education levels, so if your vet dismisses them as uneducated lunatics that is his problem because plenty of educated people are expressing their concerns (I was around in the 70s when a fellow I was studying under in my biochemistry major was rallying against trans fatty acids...the SEVENTIES...and nobody listened until a few years ago...)
Just realize the vet is working for you
and tell him/herhow you want to proceed based on your own knowledge. You can get some good info here. How many of us remembered annual rabies, annual combo shots until people had enough and the AAHA decided to change their guidelines?
This is a mainline document AAHA 2011 vaccine guidelines which should give you things to think about.
Dr Schulz who has spearheaded a reduction in vaccines with the AAHA and is a professor at University of Wisconsin
New guidelines address over-vaccination issue - chicagotribune.com
Now vets will shake their head if you want to space things out and think you are silly but it is no hardship on them but your vet likely will NOT have individual parvo and distemper vaccines so the DHPP at one time, the Lepto at another and the rabies at yet another will still provide the same protection but not put such a burden on the pups immune system all at once same time. Individual vaccines are available for distemper, parvo and lepto but many vets do not stock them.
Just to be clear - if you give 2 lepto shots NOW, after a year your dog is NOT protected and if you go out two more years it would take 2 lepto shots again to reimmunize. You can read the lepto protocol. Puppies and small dogs are more likely to have a reaction to lepto. A 5 lbs dog get the same shot as a 150lb behemoth. It also discusses 4 servovar vaccines vs. 2 servovar vaccines and some DHLPP still have only 2 servovars.
Lepto has improved but it and rabies are both shots more likely to cause extreme reactions and it just makes sense not to give them at the same time....