Why is there an indentation in bottom of wine bottles?

The hollow bottom has nothing to do with easier pouring but only with glass STRENGTH.

Glass is weak in bending (not many 12ins rulers about!) but strong in tension and compression.

The "cone" at the base is under compression form the pressure inside the bottle and this puts the end of the bottle (the tube part) into tension. If the base was flat, instead of cone shaped , it would 'bend' from the pressure and thus break.