With Day of Black Sun, you can destroy cheap, aggressive creatures at a reasonable cost while leaving your larger threats untouched
Cost-reducers like this appear in multiple tribes, but few are as efficient as this or provide additional upside to boot
If Foreboding Steamboat leaves the battlefield before its first triggered ability resolves, the chosen creatures won't be exiled at all
Over time, more and more powerful cards also require specifically colorless mana instead of or in addition to colored mana, especially Eldrazi like Ulalek, Fused Atrocity
Pacifism really hit the flavor of white pretty well - it was removal that wasn't really permanent removal (Pacifism itself could be removed), but it kept the creature at bay indefinitely
Japan Showcase cards return with Foundations