When you publish your crosswalk app, you have to upload 2 APKs one for ARM and one for x86 to work on the most devices. The build email will have a link to a zip file with both of them. The build email also has a link to page that describes the extra step to publish multiple APKs. It is only a few extra clicks and an additional upload. If you have published with crosswalk, please publish both because when you only publish the ARM APK, it won't work on Intel phones and tablets.
For those of you who have published just ARM, I am curious about why. Not aware that you need to publish both, don't know how, or some other reason? Please send me PM or post here.
Recently, google has announced some APIs that might make it possible for us to automate the uploading of APKs to google play. We hope to add this feature to XDK soon so you can skip the download/upload of APK and other assets--there would be a button on XDK that would do most of that for you. But we recognize that some of you prefer to sign yourself so we still need to understand what it will take to get developers to publish ARM & x86