A pushbike has some distinct advantages.
1) Easy to repair.
2) No carnet!!!
3) No fuel other than food
4) Can be taken on planes, buses and trains, often for free.
5) Inexpensive
6) Abandon-able (less expensive and.... no carnet!)
7) Ecological
8) Easier border crossings (no customs documents)
9) No vehicle registration issues
10) No insurance issues
11) Can almost always be taken into hotel rooms.
12) You can go places other vehicles cannot (Angkor Wat Mountain Biking Photo Below)
13) In the same way that motorcycles allow a better connection with the average person than car/truck travel, a bike encourages and even greater connection with the average person.
We've done both motorcycle and bike travel, and enjoy both. The bikes we used in Southeast Asia were purchased at thrift stores in the U.S. My bike cost $29 and Amanda's was $14.99. 1980s mountain bikes are the perfect expedition touring machines.