The Openlayers plugin can only deliver the tiles if they are on the server. The maximum zoom level is different for the various maps. While some servers are restricted to a certain zoom level, bing has higher zoom levels only for urban areas.
You can get an overwiew of the quality from : http://ant.dev.openstreetmap.org/bingimageanalyzer/
Using the original bing website, you may notice that the display changes from
aerial imagery to
birds eye imagery when zooming in. The plugin does not use the birds eye imagery.
For those reasons, you will not see detailed maps everywhere.
Some software tries to do an extra zoom on the last available level, but the plugin does not. We had serious trouble with Google satellite images that were misplaced when trying to overzoom.
You might be used to get a
no tile available pink tile, but that would not help you much further.
Try one of the other available services from the Openlayers plugin, or look out for a WMS service of the desired area.