You most certainly can save weight without abandoning the "DSLR concept". I typically shoot with a D7000, which is not really a heavy camera. I also have a D90 and a D50. They are all basically the same size and weight - so I just use the D7000 for everything. I bought my son a D3100 for Christmas this year, and have been taking snapshots with it during the holidays. For that purpose, it's wonderful,...so small, light and simple. At 24MP, it makes nicer crops than my D7000. With good lighting, and for anything that doesn't move, it's much more fun to use than the D7000. I know we're not talking about the same class of camera here, but there is clearly also bigger difference in weight between carrying a D600 and carrying a D4, than there is a difference in IQ.
I have resisted the siren song of big f2.8 zooms for years for that very reason. I can't imagine carrying/using them for anything other than the specialized circumstance when nothing else will get the job done. Those circumstances are just too few and far between to justify the expense.