Good question. Unfortunately, they are both very different concepts.
A silencer (or suppressor) works very much like a balloon, in that if you prick a balloon with a pin, you can hear the 'pop' it makes, but if you let the air out slowly, you don't hear the same noise. Silencers work on the same principal, as the bullet leaves the gun barrel, the pressure built up from the ignited gunpowder is released slowly through the silencer as opposed to being released all at once from the gun barrel.
With leaf blowers, you are hearing a constant whine of turning machinery. Perhaps, there are ways to quiet that down, but it may be a matter of economic returns, thus making a silent leaf blower expensive.
That's something that caused our local inventor Yknot Justashuddupperdeface to get into deep trouble from the human rights commission recently, after he got caught trying to attach numerous forms of suppressors to his wife's mother!
He claimed that she had a similar pitch in her voice and was a sucker for leaf blowers who had volunteered to help him create a noise-proof MIL Model!