Why is x-wind an engine limitation?

[cwatters]

http://www.skybrary.aero/index.php/A..._(HF_LOC_WX_AW)

Recommendation No.: 15/2009

To the Luftfahrt-Bundesamt (German Civil Aviation Authority) that:

The Luftfahrt-Bundesamt should ensure that maximum crosswind take-off and landing speeds are set for German Air Operators. Within the context of flight operations management, all air operators should examine the handbooks provided by different aircraft manufacturers for different aircraft types and study how the handbook wording maximum crosswind demonstrated is interpreted and acted upon. When indicated, an instruction should be issued based on EU-OPS 1.015 to require that maximum crosswind values be set for crosswind take-offs and landings.