Different extracts do behave differently. They've all got different ingredients, for a start. They've been mashed differently. They've been concentrated to different levels. It takes either an afternoon of internet research or lots of pre-internet experience to figure out what's what.
For example's sake, here are some things I know off the top of my head - Muntons extracts ferment quite dry and thin. Briess extracts have a proportion of Crystal malt in them, no matter how pale the label says it is, and generally ferments with a fuller body. Alexander's is 100% US 2-row Klages pale malt and is very neutral, leaving little impact on the beer.
Cheers,
Bob