Break one aluminum rack - * with it collapsing into your wheel and throwing you from your bike in heavy traffic - not fun - still have the scars to this day * and "bomb proof" may be a major concern of yours too.
Albeit, 3lbs. does seem heavy for a steel rack.
"Things look different from the seat of a bike carrying a sleeping bag with a cold beer tucked inside." ~Jim Malusa
2009 Trek 520-Brooks B-17 Special in Antique Brown
2010 Surly Long Haul Trucker-Brooks B-17 Standard in Black
1983 Fuji Espree Single Speed-Brooks B17 British Racing Green