[BioC] mean versus linear model?

[Simon Melov]

Not being a statistician, I was wondering if there were a 
straightforward answer as to why using a linear model was "better" than 
a straight mean in limma when estimating the average M value across 
multiple chips. I believe that the regression analysis is supposed to 
be less influenced by outliers, is this the chief reason the linear 
model is implemented?

thanks

Simon.