"Standard" jobber-length drill bits uaually have a 118 degree included angle between the flutes. They're good for drilling plain steel and some alloys that are harder than normal. The 135 degree bits have a little more aggressive cut in softer metals such as aluminum or brass, and don't do well with tough alloys. As the angle gets flatter and the speed is slowed down, harder metals can be drilled more efficiently.
Jerry
It's the other way around...135-140 degree drill points are what is used for tougher materials. Here’s a good article on drill point geometry:
http://www.mmsonline.com/articles/choose-the-best-drill-point-geometry
