It depends on the lav mics and how they will be used. The majority of lavs you see on TV or in theatre are used as radio mics. Connectors CAN be 3.5 mm (usually for cheaper transmit packs) but things like mini-XLR, LEMO and a host of others. In the radio mic world, the transmit pack provides bias power for the electret condenser.
Sony used to sell ECM 77 lavs designed for cable use. these had an adaptor at the end of the cable, allowing the mic to work from AA batteries or from standard phantom from a mixer.
I'm a fan of lavs for the right purposes but it can take some fiddling and changing of connectors to make them work in a "normal" situation.