If you already have your hands on one of the earliest Android Wear smartwatches and are itching to get a hold of some dedicated Android Wear apps, you might want to hold of cashing out on a new paid app for a while. At the moment, installing paid Android Wear apps are silently failing due to an encryption mechanism in Android that is used to prevent paid apps from being pirated.
Android Police explains the relation between App Encryption and installing Android Wear apps. Since these smartwatches don't have Internet connections of their own, the only way to install apps on them would be to either sideload them, which isn't officially recommended, or to install via a smartphone. App developers will need to package Android Wear "mini apps" with a regular Android app. Once the regular app is installed, the Android installer will extract the Android Wear app and send it over to the smartwatch via Bluetooth to be installed. Sounds simple enough, until you get to the case of paid apps.
The problem here is that the App Encryption mechanism hasn't been updated to take into account the existence of Android Wear. Normally paid apps are encrypted with a device-specific key that protects the app from being cracked and pirated. However, the Android Wear installer doesn't know how to handle the case of extracting the Android Wear app from the encrypted paid app and simply aborts the installation process. As free apps don't get encrypted this way, they can be installed just fine.
At the moment, Google has not yet made a public statement about what looks like an oversight, but it is likely already aware of the issue. Although there are possible workarounds for developers to provide installable Android Wear apps and still get paid, it would probably be best to wait for an official fix, or at least a word, from Google and users are advised not to make any purchases just yet. It is somewhat good that this bug was exposed while Android Wear smartwatches are still shipping out, but Google should issue a fix as soon as possible before this becomes a PR nightmare.