The step is not supposed to affect the user input, but only the spinners. This is the default behaviour of the NumericTextBox widget, the functionality that you are looking for is available in Kendo Slider.
Regarding validation, to enable it you will have to add the data-type="number" attribute to the corresponding input. For example:
For convenience I have updated your fiddle, please check the result: http://jsfiddle.net/valchev/Ns6sd/9/
I hope this helps.
the Telerik team
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