4 Ohm vs. 8 Ohm, what does it mean.....

It's a good question and typically misunderstood by many--even some designers. You are correct in thinking that the higher load would be more "accurate". It has less demands on the amplifier and is easier to drive. However, the trade off is that it has less output per watt that it's 4 ohm counterpart. For this reason many manufacturers reduce (or trade off) the load for higher output. In addition the load (4 ohm vs 8 ohm) that you are referring to is the "nominal" impedance of the speaker. Many speakers rated at 4 ohms can go down to 2 ohms at certain frequencies or even lower. This can create very difficult loads to drive and they can be very demanding on amplifiers. So, as someone once said to me after a lecture, "what's the take home pay?" These nominal impedances have little meaning. You need to see what the impedance curves are throughout the range and once you know these you can narrow down the amplifiers that might be appropriate for that speaker. A speaker with relatively flat impedance curves even if it's rated as a 4 ohm speaker will be easier to drive than a speaker that has wild swings through the frequency range.

also keep in mind that Tube amplifiers like higher impedences such as 8 ohms or higher, were as Solid State amps can drive more power into lower impedences such as 4 ohms. although even some of the best Solid State amps can still have trouble driving very low impedences such as 2 ohms. speakers that drop down this low I would stay away from because they will limit the choice of amplifiers you can use on them.

I absolutely agree with the above responses from artistic Audio and from Rives, The Manufacturers have focused on 4 ohm speakers to market them more effectively. They sound louder in the demo rooms than would an 8 ohm speaker at the same electronics setting. I suggest taking a sound level meter with whem auditioning speakers. Also bring your own music and don't rush the demo. Take your time and stop back a second time if necessary. Better yet, take the speakers home because the room is a big factor in the evaluation process. Good Luck