Yes, all defaults are recommended. If you feel it should be different, please create a bug report with your motivation.
TIA
I think that spam filtering is a bit more nuanced, and doesn't lend itself to a single universal default configuration.
A default SME server, for example, has dnsbl, rhsbl, (and now) uribl disabled -- all standard and very effective spam fighting tools.
Rather than defaulting to the optimum spam fighting configuration, SME server defaults to a configuration with the best chance that email will be received successfully. Once the system, ISP, and DNS have been properly configured the server admin can enable the various tools available to improve spam filtering.