The philosophy of many OSR games is keeping it simple so someone can create a character in a few minutes and start playing. Or in golfing terms 'grip it and rip it'. The death ratio is fairly high, but making the characters takes little to no time and there is no shortage of handy tools out there created by all the OSR folks to help things along.
Simplicity of play is fun, but the group I run in likes a little more complexity. OMG. That's right. You heard me. I like a little complexity to my game. I prefer to be able to make my character unique not a cookie cutter class guy. I want options damn it. Maybe this is because I player GURPS for many years before getting involved with the more old school philosophy of play. For short run campaigns or one shots, the grip and rip it style is great, but when I am going to play a guy for a while I like growing beyond the narrow confines of a class definition.
I like being the fighter with that one little magical power that gives him a slight edge. Maybe all he can do is create a flash of light, but it's enough to give him a slight edge for a few seconds. Maybe a thief who is an expert at manipulating people, who can talk to people and get vital information for his next job. Or a mage who has contracted some horrible disease, he suffers from the physical scaring while most die from it. The sight of him makes others run for the fear of contracting the disease.
Can any of these be put into any retro clone game...sure, but the GM will need to statistically figure out the numbers. While other games have these different effects statistically figured out. Now brace yourself, but this does happen, some GMs, if it's not in the book they will not allow it.
I play more than I GM. GMs have all this room to play with to create new critters, cities, treasures of wonder and a new bagel if they choose. As a player I like to have a little room to move around also. Allow me to be creative and move my character into a direction not normally taken. Beyond the narrow scope of a class based system. I want to play in a large field and run this a way and that a way. Explore what my character can become within the world the GM created. I promise not to break your world.