Difference between angle grinder and circular saw
Different 


power
gearing
speeds
collets
tool diameters
direction of forces
means of use
climb vs conventional
accessories
ability to sand or wirebrush


I think even if you managed to fit a sawblade on a grinder, you would have a completely uncontrollable tool that would be impossible to successfully engage to any work except for cars full of lost college students who make very poor decisions and scream a lot. While that may sound like fun, in the end Final Girl will kill you.