If you have the resources, you should follow the guidelines for whichever platform the app is on.
In the past many companies considered iOS to be 'the market' and only made Android apps as an afterthought. As a result, they often simply built an iOS app in Android to save them time and cost. This wasn't done because it was a better way of doing it, just a faster way.
As a side note, the Android operating system, and the associated Design Guidelines have evolved and improved massively over the last few years, whereas iOS has remained relatively unchanged. Android has become the better platform (in my opinion), and the largest (both in terms of users and in terms of revenue). So it is most definitely worth building a well designed Android app. In fact, Android is where most applications should begin, with iOS being the afterthought.
As a heavy Apple user, this is a grudging admission.