Except that the choice wasn't made in the past to allow for future expansion:
http://en.wikipedia.org/wiki/ASCII
"The committee considered an eight-bit code, since eight bits (octets) would allow two four-bit patterns to efficiently encode two digits with binary coded decimal. However, it would require all data transmission to send eight bits when seven could suffice. The committee voted to use a seven-bit code to minimize costs associated with data transmission."
The fact that a lot of data transmission systems in the 60's where not 8-bit clean also probably played a factor.
What really happened was that the future took advantage of the fact that ASCII is a 7-bit code to be able to create the UTF-8 encoding in such a way that UTF-8 is backwards compatible.
