The requirement to have a Mac to build from iOS is due to the supported platforms for Apple's Application Loader: it's Mac only. Even if we did add support for signing your iOS app on Windows you would still need a Mac to submit it to Apple.
OK . . . That answers it. I'm assuming that means I can't build an app for my iPad on my PC and that I'll have to switch to my Macbook Pro for an iOS app. Does that also mean I can't create the articles on my PC (Indesign)?
Sorry, Louise. I must have been tired when I wrote that message. I think you were using the signing tool used to sign Android apps for DPS. The signing tool is available in the Apps section of the Portal, in the upper right corner. You should have a signing tool that looks like this:
It looks like you're using the web-based signing tool for DPS App Builder. Have you downloaded the signing tool from the DPS beta resources page? (www.adobe.com/go/dps_beta_resources) Make sure that you are using a Mac computer and that you have downloaded the signing tool from the Apps section of the Portal.