The a=b&c=d syntax is part of application/x-www-url-formencoded which was a Mosaic invention, and came after query strings. [0] [1]

[0] http://1997.webhistory.org/www.lists/www-talk.1993q3/0812.ht...

[1] https://web.archive.org/web/19961220100435/http://www.ncsa.u...