Ok this whole receptor thing has been beaten to death.... Jesus Christ.... it's like you heard of this word and you keep repeating it without even knowing what the hell it means.
I don't mean to flame anyone, here, let's get that straight.....
Some AAS work by binding to the ANDROGEN receptor (test, deca etc) and some are thought to mediate their effects by other pathways, possibly by antagonizing the glucocorticoid receptor(D-bol, drol etc).
Now if the above is greek to you, then please do some fucking research and don't just use words you don't understand!
Now concerning the original poster's question, the reason why newbies don't need to use a lot is quite simple:
well, one is that most newbies are nowhere near their genetic potential, so they will grow even with one Sustanon per week, but we'll ignore that,
the main reason for not using a lot of gear is that your body reaches a maximum rate of growth with X amount of gear and using anymore is a waste of money, and mostly an unnecessary health risk, since the more you use the more side effects you get. Basically, using too much gives you more sides with no added gains.
Hope that answers your question