What is it with clicking on pictures and language learning?

It just dawned on me today that there's a good handful of language-learning tools out there where clicking on pictures is an important part of the learning method. For example:

• Rosetta Stone
• Rocket Languages (this blog's favorite astroturfer)
• My-Language
• Livemocha
• Busuu

(And if you know of any others, drop a line in the comments below.)

This seems to be a pretty common method. Is everyone just playing follow-the-leader (i.e., following Rosetta Stone), or is there actually some science to back up all this fervent picture clicking?