You are probably giving up a little accuracy in the following:
1. No free floated barrel. - can be added for about $150+ (all in).
2. Shorter barrel (I know, actually giving up velocity, but that can translate into longer range accuracy). This is an expensive modification that probably isn't worth it.
Also what you are not getting that has nothing to do with accuracy:
1. No chrome or nickel BCG
2. Possibly no chrome lined barrel
3. Better stock
4. Better iron sights (can be fairly expensive, but can be added)
Also Some of the aluminum (receivers, might not be 7075 - I doubt this matters all that much.