For your average business app, yes, I agree, however there are a lot of apps I use on my iPad that have essentially moved this "custom skin" UI into elements in a full-screen wrapper and they look and work wonderfully. There are also lots of smart devices that have hyper individualized UIs, modern cars, anything in the audio realm with a screen, plenty of examples.

But yes, you're showing a series of forms to fill out? Use the platform native controls and make it work perfectly.