Yep that is true but the benefit is like i pointed out earlier, humanly readable MC source instead of "aa.bb.xyz()" you might get "AwesomeClass.AwesomeClassChild.AwesomeFunctionToMakeAwesomeThings()" and if you are in the market for awesome things you wouldn't miss that for SURE.
And MCP does decompile, deobfuscate and recompile and reobfuscate just fine. As long as you can fix a few errors that crop up along the way. So that's the price you pay for readable MC source code. You fix a few errors or apply the appropriate patches (since others have already gone through the hassle of fixing them before)
Once upon a time i did all my modding in obfuscated MC classes. The whole "ea.tm.yp.oop()" ordeal. Something as simple as altering the ore distribution was quite an advanced feat as you had to look up each ore type. Then i tried MCP and all of a sudden i didn't have to do any lookups and remember any "ga.y" names.