Can I install apps on Lion without using app store?
Not true - mean sure can install apps from dmg.

The Lion remain a full-blown OS, with all common functions, like Terminal.app, root access, Developer system, and so on. When here is no way block installing applications if you will have a root access, so Apple sure will NOT TRY do this.

The following is only my opinion:

On the other side - most of developers will sell their apps via AppStore (because it is easy), so here will be less "demo downloads" (what was possible activated by simple serial#). IMHO, over the time will be here more and more application in AppStore in two versions, like for example:


SudokuLite.app (like current demo versions) - free,
Sudoku.app (full paid version)