You make a good point. Specialized wouldn't implement a recall based upon outliar failures from owners that remove their steerer expanders.
I believe a point to be made however...is something called an interaction of contributing factors. If you have a weak design in combination with expander removed...perhaps in combination with strong rider...you have a perfect storm for failure.

What typically happens is...from a guy that developed safety critical products:
- Failures occur in the field which generally result in people getting hurt.
- Failed parts are immediately procured.
- Parts are evaluated on a microscopic level
- Parts are compared to current manufacturing practices. Part failure can be a function of manufacturing defect or design defect. If design is problematic, tooling changes are enacted. Testing is devised to replicate failure mode.
- Also, generally for safety critical product, products are sampled and tested from the production line. In this case they maybe even X-rayed at a high sample rate....sometimes even 100% as process control is improved upon.
- Failed parts are attempted to correlate to a known mfg. time interval
- Recall strategy is formulated
- Recall implemented.