The thing is, I am often very confused when I want to do things on a Mac. Maybe it is just because I am used to the old fashioned way of just attaching a file to my email. Like with the right click, files always work the same way. Unless every app comes from Apple (which is probably their goal), not all apps will adhere to my expectations in the same way. And even Apple will probably have a hard time to pull it off.
Some tasks simply are complicated by nature. I don't think all use cases are isolated. For example mailing an image is not an isolated use case (or rather, would it really be less confusing to have different apps for mailing images and mailing text?).
Since when can't you mail images or other files with OSX? Just drag and drop a file into your mail and you're good to go. There's also the "attach" button when writing a new mail.
How do you drag a photo there if it is in iPhoto? Where does iPhoto store it's photos? Is it even legal to just copy fotos out of the iPhoto folder?
I also tend to have problems on OS X because the finder sucks and dragging files to the task bar -> window opens -> drop on window often does not work for me (I suppose it should work?). If you open the finder, it hides the email window...
Just drag the photo from iPhoto to your new mail. Be strong, there's a lot of good magic involved(;
Also, iPhoto stores the pictures pretty conveniently as you might expect: ~/Pictures/iPhoto Library. And of course you can copy the files out of there.
And finally, you might want to get a screen that can fit a new mail and a finder window next to each other. A 13" monitor should do that just fine, btw(;
Do one thing and do that well, I say.