Thanks for the screenshot; you've spotted a real bug here.
To confirm what the picture shows: both fields have identical settings (Value 3.1415, Minimum 0, Maximum 100, Increment 1, DecimalPlaces 2), yet the Web one displays 3,00 while the desktop one displays 3,14.
The desktop behaviour is the intended one. Increment only controls how much the up/down buttons add or subtract, and DecimalPlaces only controls how the value is displayed - the stored value keeps full precision, so on desktop Value reads back 3.1415 even though the field shows 3,14.
The Web NumericTextField currently goes further than that: it snaps any value onto the Increment grid (so 3.1415 with an Increment of 1 becomes 3) and rounds the stored value to DecimalPlaces as well. That's why it displays 3,00, and it also means code reading Value on the web gets 3 instead of 3.1415. (The smaller visual differences - the spinner button styling and the lighter placeholder text - are just platform styling.)
I've logged this as a bug and it will be fixed in a future release. As a stopgap, choosing an Increment that divides the values you need (0.0001 for example) together with enough DecimalPlaces (4 or more) lets the Web control hold precise values in the meantime.
Thanks again for the clear side-by-side comparison - it made this easy to diagnose.
