Yes, I'd think the decisions are deliberate.

Floats follow printf(), this is from the manual for 'e':

  "The exponent always contains at least two digits; if the value is zero, the exponent is 00."


And decimal follows the specification at 
http://speleotrove.com/decimal/ .


Of course Python's format() could decide to override the specification, but it would lead to more code complexity.

But I don't think that mixing float/decimal output is a common use case.