Jeff, I had similar concerns as I live right over the fault line (I am about 15 mins or so from John), and 5 manufactures I inquired with recommended not anchoring or left that as optional (it was on my questions list when I shopped around). The only ones that recommended anchoring are for larger non hobbyist, commercial heavy weight capacity. I think the anchoring on commercial settings definitely makes sense as there will be a lot more risk of the device getting bumped hard by a car, or other equipment which I do not think come into play in a hobbyist setting. OSHA and other requirements may also play a factor.
I agree with you and believe on a commercial setting there are more requirements hat may dictate the need to anchor or floor mount. bear in mind some hobbyist lifts like Backyard Buddy which seems highly recommended by some. BYBuddy has completely removed\omitted the anchor hole locations mentioning it is not needed with their lifts.
I hear what you are saying, but in an event of a quake it may be better to allow the assembly to fluctuate, rather than anchored where a considerable crack or slab collapse would allow enough move that could jeopardize the whole assembly.
If you look at any manufacturers FAQ they recommend the lift in a Hobbyist type approac to be free standing rather than anchored.
http://www.directlift.com/FAQ.aspx
•Do I have to anchor my lift to the floor?
We only require our two post lifts to be anchored to the floor.
Four post lifts do not require anchoring unless floor slope is greater than 1/8” per foot.
http://www.gregsmithequipment.com/4-Post-Lifts_3
Q: Does my lift come with anchor bolts and/or the hardware to mount it to the floor?
A:Most of our commercial grade four post lifts come with the appropriate number of anchor bolts to mount the lift to the floor.
It is important to note that our Hobbyist four post lifts are free standing and do not need to be anchored to the floor. (Anchor bolts are available for these lifts at an additional charge). The Customer will be always be responsible for providing the necessary hydraulic oil for the lift.
Note most manufacturers that are certified received the certs with them tested without being anchored. IE Bendpack.
My suggestion is, whoever you buy the lift from, check what they recommend
