What is the difference between the progress of low and high intensive meditators? What is the difference between the progress of "low intensive" meditators as opposed to "high intensive" meditators? 
  By low intensive I mean like a meditator who has never been to a ten day intensive retreat and spreads sitting time over a longer period of time. By progress I mean Vipassana insight progress, Jhana progress or any other kind of meditation progress in any tradition.
I guess the short answer is that in general the more intensive meditation practice you do the more familiar you will become with the jhanas and the more insight you will experience. Larry Rosenberg in Breath by Breath does say that retreats are needed to experience certain levels of insight. However he does emphasise practice in everyday life even more.

However I don’t think things are that simple....

Intense practice isn’t necessary for insight

Willougby Britton in the Dark Night project has been analysing negative effects of meditation i.e. the dark night. This is a state that it’s possible (likely, certain???) to get to with a certain amount of practice. She says the two populations of people who appear vulnerable to this are


Super intense meditators typically in their 20s to 30s who go to
Asia, ordain and then spend 12 hours plus a day meditating.
Middle ages practitioners who have been meditating for an hour a day for 10 to 20 years an maybe going on retreat once or twice a year.


The point being that both lower and higher intensity mediators do progress along the path but a different rates. The second population is doing enough and has a real and effective practice.  That said the second group is still pretty dedicated but not outrageously so.

Retreats aren’t necessary for insight

Dipa Ma, the Buddhist master taught a nursing mother enough mindfulness practice that she attainted the first stage of realisation without leaving the house. So long retreats aren’t an absolute necessity for insight. 

Even formal meditation practice isn't necessary for insight

The founder of dharmaoverground, Daniel Ingram, said in this Buddhist Geeks podcast that people can and do have genuine insight from yoga practice, on long marches in the military or even breath control classes for actors. So formal meditation isn't even necessary for insight.

So ...

I've heard the relationship between insight and meditation described in terms of being struck by lightening. If you hang around on windy moors in thunderstorms (i.e. meditate intensively) you are more likely to be struck by lightening (insight) than if you sit in front of a TV set and never go out (i.e. never meditate). However people that do habitually sit in front of the TV do occasionally get struck by lightening. Similarly people on windy moors in thunderstorms may never get struck no matter how often they go out and jump up an down with a foil hat on. 

There's no guarantees - meditation just increases your chances. To use another analogy - you can't force plants to grow. You can only dig the soil, water the earth and put the best conditions possible there.