The Dutch situation seems to have been changing a lot lately. I crossed under the Amsterdam TMA with mode A/C with no problems a few weeks ago, but from June 5th they've made almost the entire country a mandatory Mode S area (see AIC 07/08) as well as the requirement in the Amsterdam FIR unless below 1200' in class G. But ENR 1.6 states that VFR traffic is allowed to have mode A\c only and no transponder required below 1200' in class G.
So my interpretation is that, at least for a while, you don't need Mode S outside of the height and time limits listed in the AIC, but it need some careful reading. An earlier AIC effectively banning Mode A/C only was cancelled.
For Belgium though they seem to have backed off (see AIC 05/2008) and Mode S for VFR has been delayed to 2011.