i love this statement right here, if a 70,000 mile tire was going to last 70,000 miles. it can only run on perfectly paved roads in one direction with no stops, no starts, no turns, and only going one predetermined speed based on the rating of the tire. (typically i have heard it is 35mph). Change any of those factors and a 70k mile tire will not last that long.
I typically get 10k miles out of a set of tires, regardless of if the tires are on my aveo, my audi, my vw, cavalier, r32, toyota truck, heck I've owned over 150 cars, and probably put at least one set of tires on all of them. The oem tire that came on my aveo lasted 3000 miles because of my driving style, my current set of sunny tires ($45 each) went 15k mostly highway.
The floating suspension is a copy of vw's design used for almost 40 years. To the point that I just stuck vw vr6 strut mounts in my car to test them out. I run vw coil overs, and you can replace your rear axle bushings with vw bushings when they wear out. The design between the bolt in plate top mount and the floating top are only slightly different, being the strut tower becomes part of the suspension, where in design, the bolt in struts you are essentially unbolting the top of the strut tower with the strut. In fact quite a few bolt mounts have the same mount design inside that plate. It is also different depending on how the rest of the suspension is designed.
IF you want to have a real debate about tires and how long they should last, post up the specs, brand and price you paid for the tires. The post your typical driving style, what the wear is on the tires, pictures, alignment print outs, and the road conditions and type.
But that is only If you want to have a REAL tire debate, if you want to have a suspension debate, then we can research the suspension designs of all the "better" cars and compare just the upper strut mount that you blame in comparison.
In all honesty, 18 tires is also kind of a number game, that is only 4 and 1/2 sets, since tire companies never replace one tire for this reason or that. You have gone 45K miles on 4 1/2 sets of tires, your right in like with my 10k mile per set of tires mark. Which leave me to believe you drive a little fast, in stop go traffic, and make a lot of turns, as well as accelerate with the wheel turned which chews off the edge of the tire, which we could prove if we could see your tire wear.