I'm not sure where audiophiles got the impression that LP's don't contain low frequencies, but Twl's comment is on the money. I have some LP recordings of pipe organs which have frequencies that reach as low as my pair of Vandy 2Wq's can reproduce, which certainly means down to the 20-Hz range. I have also read liner notes on several of the Telarc LP's that I own that state there are frequencies down to 16 Hz.
Having said all this, that does not necessarily mean that a given person's analog system will be able to accurately reproduce frequencies down to the 20-Hz range. The turntable itself must be rock solid and well isolated from acoustic vibration; and the tonearm/cartridge combination must be able to accurately track the wide, low-frequency undulations of the LP's grooves. Extreme low frequencies require very wide groove on the LP, and this is a severe test of tracking ability.
Having said all this, that does not necessarily mean that a given person's analog system will be able to accurately reproduce frequencies down to the 20-Hz range. The turntable itself must be rock solid and well isolated from acoustic vibration; and the tonearm/cartridge combination must be able to accurately track the wide, low-frequency undulations of the LP's grooves. Extreme low frequencies require very wide groove on the LP, and this is a severe test of tracking ability.