In Sri Lanka earliest writings (which were mostly religious) were preserved first in the mediums such as Palm leaves, and the alphabet clearly shows that influence. As the top comment points out, making sure that you do not damage the script was a pretty important concern, and rounded letters certainly helped. If one studies the evolution of Sinhalese (and Tamil) alphabet it can be clearly seen that things got curvier as the alphabet developed from earlier Brahmi scripts [1].

[1] http://www.akuru.org/developsinhla2.htm