I think it's a bug in RhoMobile. It'd be nice if Motorola fix this issue. We will raise this issue with them to get an answer.
I suspect this might be related to the browser implementation on the device itself. I have used "number" and it works fine with decimal points on a Motorola Solutions TC55, but on a Samsung S4, the soft keyboard that comes up does not even have a decimal point on it. So it seems like different phone vendors have implemented this feature differently, and some of them do not support decimal points in a "number" input field.