My first inclination is to say that it's a matter of skewed perception. There are a multitude of factors that go in to this, including whether your acceleration on a bike tends to be steadier or come in a tiny burst with each pedal's downstroke (influenced by bike geometry and weight) and the fact that sometimes we might perceive a 1% gain in speed to be really big, and other times it will go unnoticed.

Secondly, I've ridden different bikes and I think the geometry can have a huge effect on how much power your feet put down to the pedals. Your muscles are just not able to give anything close to their optimal effort if they're not positioned correctly. (This means that it's possible another person would be really fast on that bike because it fit their body shape/size better.)

Thirdly, tire pressures and sizes are important, but not exactly in the way that people usually think. Some wide tires can be run at pressures that are rather high (i.e. 90 psi) while sometimes narrow tires are actually used at pressures of 90psi or less. To my knowlege, there are only two times that anybody has tried to do a controlled comparison of a bunch of different tires, and the results were surprising: you could get good rolling resistance by running narrow (about 1 inch) tires but beyond a certain point higher pressure meant more rolling resistance (vibrations/bumps slowing you down, probably) and wide, (about 2 inch) high-pressure tires gave even better rolling resistance. Rolling resistance for narrow tires at low pressures was worse than for wide tires at low pressures.