Copaslip and all similar anti-seize compounds contain loose flakes of copper mixed with grease. Unlike some plain greases that might dry up or disperse, these metal flakes are guaranteed to stay put until it comes to disassembly, when they help the two components slide apart. In other words, it prevents seizure. This is something you may need on bicycle parts that are left a long time before removal - and this can include bottom brackets.
EDIT: Copper also may make galvanic corrosion less likely (depending on the metals), and the grease in the product keeps out electrolytes anyway.
I don't think a reputable company like Finish Line would claim it was suitable for all metals if that was blatently untrue. It's common practice to use it for aluminium and steel components in titanium frames, so it should be equally good the other way round, etc. Anyone in doubt, however, can use an aluminium-based anti-seize product instead of a copper one.
"Prevents cold-welding, galling, and seizing of metal to metal contact parts, especially those subject to extreme pressures and moist conditions such as bolt threads, seatposts, pedals, bottom brackets, etc. For all metals, but essential when attaching reactive metals like titanium, aluminum, and specialty alloys and magnesium"-
http://www.finishlineusa.com/products/ti-prep.htm