Let's not adopt the Microsoft approach and assume that users are too stupid to work out that they need to look in the directory in which the program is installed or lack the initiative to make links to folders that they frequently access.
This is going a bit off-topic, but the issue is not that users are "too dumb" to look there. The issue is that software is generally installed in locations that should be considered read-only.
On both Windows and Unix systems (including Mac OS X), the system-wide installation locations for software are only writeable by administrator users, a regular, limited user account doesn't have write access to them. It's both an issue with multi-user systems (such as a computer shared between three members of a family) to avoid mixing different users' data, but also an issue with security/safety, to prevent program files from being changed unwittingly.
In the specific case of Mac OS X, if you have digitally signed software, an entire application bundle is signed as one unit, and changing any one file inside a signed bundle invalidates the signature of the entire bundle: The bundle should be considered one immutable file for most purposes. The same thing applies (should apply) to other program installations.
However, "portable" software is a different issue. Portable as in, software you can carry with you on a removable medium. Dwarf Fortress is designed in the portable model, which happens to be mostly the same model that almost all PC games before the advent of Windows XP used.
In short, there's two good reasons to keep user data separate from program code: It makes it possible to better tamper-proof the code, and it lets many users share one copy of the code without sharing their data.
Fair point, though I addressed some of the issues in my original post and some don't really apply to DF. Forgive my ignorance. It's an definitely an interesting problem, any way. I suppose it depends if you prefer to have all software using one system that is easy to break, unwieldy and limiting but uniform, disk-space-efficient and (for some other programs) more secure. And indeed, as you say, the situation for a multiple-user computer is different if space is at a premium and all users want the same version of DF but can't be trusted with each admin rights and each others' data, though it would, as you say, be different for a Unix(-like) computer with a superuser.
Out of interest,
also an issue with security/safety, to prevent program files from being changed unwittingly.
What sort of thing are you refering to?
The same thing applies (should apply) to other program installations.
Why? Consistency?
Portable as in, software you can carry with you on a removable medium.
As in "A portable application does not leave its files or settings on the host computer. Typically this means that the application does not write to the Windows registry or store its configuration files (such as an INI file) in the user's profile; instead, it stores its configuration files in the program's directory."? (Wikipedia: Portable application)
That's a Good Thing, but copying over, and keeping track of, saves and raws would be time consuming, error prone and irritating. Why not go the whole way and include everything in one managable folder?
Sigh... I suppose I could move DF
into the save folder that it created.
Edit:
and making DF properly installable is something
(my emphasis)
What do you mean by "properly" installable? And what would it actually add apart from the ability to suggest an install location and spam the start menu and desktop with links?