Did you consider that is the case because Challenge tires suck?
I saw some Strada Bianchis at a swap. They felt like a garden hose. Just because it is big, it doesn't mean it's good.
The Strada Blanche's I had were quite supple and had a very high thread count. A bugger to mount also. They felt great in use but were very flat prone for me. I moved them amongst several bikes before giving up on them. I can not ever say they felt like a garden hose though. I wonder if there were different versions of these?