First we need to remember Joel doesn't spend as much time on his blog entries as Paul Graham spends on his. With that in mind - what did Joel mean? Joel meant at leat these two things:
a) Complex design patterns will be refactored into fewer elements. GWT is a nice try but Java isn't simplification - and you Java heads know this.
b) Optimization isn't the only secret sauce to rely on. Companies that put all their eggs in this basket get burned by companies that understand the larger problem begging for a solution. When resource scarcity relaxes, the companies that understand this will automagically appear at the front of the line.