If I'm wrong, someone will jump on this for sure, so stay tuned.
Yes, AE will create AVI files on a Mac, but you will definitely want to make them Lossless (if that option is available) or Uncompressed.... and let the next person in line convert them to AVIs in their codec of choice.
The reason: a shortcoming in Quicktime. QT doesn't have the full panoply of codecs for AVI files. It has really high quality... and garbage. No in-between.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
To build on Dave's point, both Quicktime and AVI are "container" or "wrapper" formats. Container formats describe how to store and read tracks in a file, but not how to actually interpret the streams. That's where codecs (codec stands for compressor/decompressor) come in -- they actually describe the video, audio, timecode, subtitles, etc.
You could store just about any kind of video in an AVI -- Cinepak, DV, uncompressed, h.264, etc., but the codec must be installed on the system for playback. Here's a list of codecs pre-installed on PCs: