The launcher doesn't provide a download option for the server JAR for all Minecraft versions before 1.2.5.
When creating or editing a custom profile under "Launch profiles" there is a "Download server" option displayed, opening a download link in the webbrowser for this version's server JAR file. When selecting a Minecraft version before "release 1.2.5" (i.e. 1.2.4 or lower, including alpha and beta versions) from the "Version" drop-down menu this option is missing.
In the attached images you can see it displaying the option for a selected version of 1.2.5 and not displaying it for version 1.2.4.