Do all mac apps automatically sync across devices?

You need a synching service like iCloud or Dropbox, the latter works quite well with text documents.

Settings will not be synched that way, you might have to look at "symlinks" or ChronoSync for that.

 

I think you can probably break Mac Apps down into 3 groups for Syncing.

1. Built in document sync support using iCloud. These Apps will allow you to save your documents directly into Apple's new iCloud's document service. The Text editor iA Writer is one of the first Apps to use iCloud document syncing. Any document saved with iCloud will automatically be uploaded to Apple's cloud service and then back down to any other Mac or iOS device running the same software and linked to the same iCloud account. We are still waiting for Apple to update it's iWork suite to work with iCloud.

2. Built in database support to share the Application database in the 'Cloud'. These Apps allow you to keep their database in the 'Cloud' so that it can be accessed by multiple devices. Apps Like 1Password and TextExpander are a couple of examples of these types of Application. These Apps may be updated to allow iCloud to hold the database, but at the moment both developers recommend Dropbox as the best cloud data service for their applications.

3. Any Application that creates files that are not too large (Word Processing, Spreadsheets, etc.) can be synced to any other device using a service like Dropbox.