Google Play lets app developers restrict which devices their apps can be installed on. Developers target specific device characteristics (screen size, keyboard configuration, software version, hardware specs, geographic location, carrier, etc) by specifying them in the app's manifest. Google Play then filters which users can install the app given their device configuration. Here's what Google has written to developers about filtering applications on Google Play:
How Filters Work on Google Play
Google Play uses the filter restrictions to determine whether to show your application to a user who is browsing or searching for applications from the Google Play app.
When determining whether to display your app, Google Play checks the device's hardware and software requirement, as well as it's carrier, location, and other characteristics. It then compares those against the restrictions and dependencies expressed by the application's manifest file and publishing details.
If the application is compatible with the device according to the filter rules, Google Play displays the application to the user. Otherwise, Google Play hides your application from search results and category browsing, even if a user specifically requests the app by clicking a deep link that points directly to the app's ID within Google Play.
Filtering on the Google Play web site
When users browse the Google Play web site, they can see all published applications. The Google Play web site compares the application requirements to each of the user's registered devices for compatibility, though, and only allows them to install the application if it's compatible with their device.
There could be any number of reasons, then, that your device is not allowed to download the apps you mentioned. You can gain a little more insight, however, expanding the incompatibility message to view the details. Here's what ghacks.net's Martin Brinkmann has written on the topic:
Google displays compatibility information right underneath's the install button on that page. If your device is not compatible, you will receive the following information:
Incompatible does not necessarily mean that your device's technical capabilities are incompatible with the app. While that may often be the case, it can also refer to geo-restrictions that the creator of the app has set. Apps can be released only to select countries, and if you happen to live in a country that the app is not (yet) released in, you too will receive the incompatibility message.
Now, to find out why your device has been deemed incompatible click on the small plus icon in the bottom right corner of the message.
Here you find the reason why you cannot install the app to your device.
As a last resort, consider contacting the app developers to ask for a better understanding of what makes your device incompatible.