Re: "grille on the bottom"
Yes, it is for airflow, don't set your laptop on a squishy pillow or a fluffly blanket unless you want it to slow down due to thermal loading ... i.e. the CPU throttles its speed when it starts getting hot. Older Thinkpads (T420 era) avoided this design-issue by inhaling cool air from the back and exhaling hot air out the sides but those devices were much thicker than current models due to the inclusion of optical drives (CD/DVD). I suspect the current design was adopted to make the laptops thinner. A good practice is to avoid parking a running laptop anywhere dusty or where lint may get sucked up into the machine's cooling fins, seems like common sense but a lot of people don't think about it.