Strictly speaking no IDE is needed for Squeak/Smalltalk either but, as with most other languages, programming is much more enjoyable with one. It was partially a search for a decent Python/Ruby IDE and a persistent environment that led me to find Squeak. Also I think Squeak is best described as a "computing environment" and differs from what many will think of as an "IDE". Another example of such an environment is Oberon.

PS: Squeak can be used headless. Look up Seaside for one exampe (including smalltalk web development via the browser).