they already do but the amount was lower than it is now. After recent update, base amount (before utility/bonuses) of stars gained is 500+stage*20, and gold is 200+stage*5 as opposed to 800+stage*10 and 275+stage*4 in the last version.
gee no more updates for further notice, that is very hard 4 me now. but just one more thing. maybe there should be dual (2 by 2) battles so all characters and pets gain extra experience. and also in the special shop, there should be cheats for the game like 3 times the xp or 3 times the health and maybe 3 times the money. or you could do 2 times the xp, health, and money if it is ok
 "Helixteus II"){kind=icon}
 "GemCraft - Chasing Shadows"){kind=icon}
 "Strategic Tic-Tac-Toe"){kind=icon}
 "The Perfect Tower"){kind=icon}
 "undefeated spider"){kind=icon}
 "Infinite Defence: Champions"){kind=icon}
 "MineQuest"){kind=icon}
 "Idle Mine"){kind=icon}
 "Mine Blocks"){kind=icon}
 "Battle without End"){kind=icon}
Alread on my todo-list. For now just pause it by disabling the "run in background" option and click anywhere on the page. :)