There are benefits to each. Really by doing the poured base they are defeating the purpose of a paver installation and it's ease to repair and ability to handle ground change. The poured method would be better than a poor base installation, but a proper base installation would be the best result for the dollar. The poured base is a waste of money that is not needed if the base installation is handled correctly. If they are going to go as far as to pour why not just go stamped at that point and get the most value?
My official response would be that the pour is not needed when the base is installed properly, and by doing so is a waste of money. Sure it has benefits, but when the slab cracks or heaves the patio will be much more expensive to fix. We plan on installing to industry standards or beyond and we back it with our 5 year guarantee, but really if you ever have base issues please just let me know and I'll have it taken care of... Is the other company offering to jack hammer out and repour the concrete base if there is an issue down the road?