Substrate for the temperate tank

I have noticed looking through the pics that most or all of you are using a pebble type base in your tanks rather then regular gravel substrate. Is there a reason for this? In my plans for the lobster tank build I was planning on using regular substrate as I have a erosa that likes to bury itself. If I went with pebble style gravel he wouldn't be able to bury. 

Only reason I can figure is flow. Are the requirements of flow that much higher in these tanks and needing the larger substrate or is this more in line with the natural bio type of the areas you are trying to recreate?