Lets be realistic, with prices of DSLR and P&S so close these days (cheapest Pentax DSLR K100D is $860, Nikon D40 $999), the only reason you want to buy a P&S is for portability, compactness and idiot-proof settings. Having to need to insert a flash means its better to just move to a DSLR because your entire setup would be big...one has a hotshoe mount, the other doesnt.
besides this, anything else significantly differs between these 2?
i'd choose the FZ-18 for the lens more flexible wide-angle and telephoto reach.
Actually I've tried portrait photography with just a 50 1.4, and it can be alright..Actually other than the above there's an additional reason of long term savings. Buying a FZ Lumix (or any other prosumer) is pretty much a buy all end all with a fantastic zoom range that satisfy almost everyone (unless u shoot wildlife or is a PI by profession then buy teleconvertors...). The lenses on these prosumers are high quality designs at that. Buying a DSLR however is only the beginning with lenses to buy in the future, other stuff like battery grips etc. The person buying the prosumer is very different from the DSLR buyer IMO. The ability to add a flash is a plus, of course one doesn't neccessary have to use it, but its a capability thats nice to have nonetheless (ever tried runway/fashion/portrait photography without a flashgun?).