In the article, there's a whole path from source to JVM bytecode to ARM assembly. With auxiliary goals like bytecode size. This makes it interesting to include add-double because it has a simple bytecode encoding ('DUP ADD' compared to 'PUSH 2 MUL') and it is interesting to see what the several compilers do with it along the way in terms of optimization.

Interesting info on 8086. Another approach that doesn't apply to OP's article, but does to x86 assembly is (ab)using LEA for small multiplications. At 2 clock cycles it looks competitive with shift for doubling, but can also be used for multiples like 3 and 5.