The numbers don't support such a claim.
1) Verizon and Sprint had their 3G networks rolled out while AT&T was still just boosting nationwide EDGE speed for the first iPhone.
2) Verizon and Sprint 3G coverage is much larger than AT&T's.
Those are facts, not opinions.
There will, of course, be exceptions where you don't have coverage, but overall the USA CDMA carriers simply don't need as much WiFi backup.
You must work for Verizon. All these posts backing up big Red. Seems rather suspicious to me.