Some devs have left and no longer support anything, some devs answer when they want to.  It is currently a buyer beware condition right now in the store.   

You really need to check reviews and also check the support section for each plugin you want.  Now reviews cannot always be trusted because the dev can create a different account and review their own product.  But if you see bad reviews you can use that information and also i would always PM some of the people who do reviews and ask them what they think.  

Also check the forum and youll see who is a regular poster, then if you see them post a review ask them.   Sadley you really need to do your research before buying a plugin.

There are good devs still here with me being one of them, and there are others as well.  But i wont mention them only because if i forget someone then they get ticked off at me. However they are easy to spot just by checking the forum and their support section for their plugins.  

As i said also check the support area of the plugin, if you see that the dev is not answering any question or providing support then that will give you important consumer information.

All the best :)