Why do turntables sound different?

Interesting thread. We all know table/arm combo's will sound different. I liken it to global climate change. We all know its going on but it is difficult if not impossible to distinctly say why. There are a lot of factors. I tend to like the high mass tables with air bearings in both the platter and arm as i "think" this helps isolate or protect against sound effects from non-groove sources. How much is caused by what mechanism but every link along the chain from the source (ie groove) to the speaker impacts. Even the wire choice on a moving coil is touted as having an impact on the sound. I tend to agree with the crux of many of the responses in that vibrations caused by a variety of sources will impact the sound. I know that bearing induced sound from my old Michell occurred and changed as i tried different bearing types and oil types. Even the air bearing system will have a faint sound, though much less than any other table i have heard, as i rotate the platter as even with these there still is a centering pin that does provide some contact from platter to the table base. I do also agree in keeping the table if possible in a separate room from the speakers. is this a huge impact, not sure, but i do it primarily to keep my electronics in a more controlled environment. 
Obviously these are just my opinions and not based on scientific measurement but rather from 40 years in the hobby with many different tables

Ralph, though you express your own opinion, I think that you misinform some people. You did say that there were many tables that you had not heard. Why would you choose the Technics before auditioning all of the top tables? And tonearms. And cartridges.

I base a lot of my assessments on an LP that I recorded (Canto General- using two different tape machines, an Otari and a modified Ampex 354 tube machine). (FWIW I feel that the Technics needs a different platter pad and plinth to really show its stuff).

Since I was there and have the master tapes, I have a pretty good idea of what the LP is supposed to sound like. I've heard plenty of 'tables; the closest I've heard that does Canto General properly has been the Technics SP-10 MkIII equipped with the Triplanar 12" arm (of all the arms I've auditioned, the Triplanar is one of the very few that gets everything right). I've found that the cartridge choice is less important if the arm tracks the cartridge properly and the phono preamp is stable.

I do concede that when I see a machine that ignores what I see as basic engineering principles with regard to playback, that I will be prejudiced about that machine. So I am far less likely to even audition it. I've learned that from using about 30 different machines at shows. Its not worth the frustration of getting things to sound right if the 'table isn't based on sound engineering.

As I said, according to Ralph everyone with good hearing and sense should go after the Technics and Triplanar arm. And don't forget about Atma-Sphere amps and Classic Audio speakers. Everything should be wired with Mogami cables, of course. That's the current state of the art. Yeah, that's how you lose competition not win.

Yes,  and perhaps more often built to a price point jeopordizing performance potential.  

Yet, there are those who gave up their Walkers and other high end tables and use highly modified Technics SP-10 MK III while claiming this set-up's with various arms and cartridges superiority. I would be happy to compare if I could. Most likely outcome is that it would be different with the advantages and disadvantages of either, and also a matter of taste and the synergy of the entire chain. At the highest level I believe you have to match everything, including turntable to speakers. The system should work in complete oneness. This would take enormous effort, but that's the only way. Science is science but art goes beyond it.