That is not right what I said.
IronScheme does not need a decimal number as it has a more complete number stack than .NET provides.
That said, it is probably not optimized for 'decimal' usage.
What do you need decimal types for? Using rational numbers (aka fractions) you can achieve the same (and more) with any loss in precision.
There is even a handy notation you can use. Example:
(+ #e0.1 #e0.3) => 19471113219505603967277331424215/649037107316853453566312041152512
(inexact (* #e0.1 #e0.3)) => 0.03
Make any sense?