Indeed WebHelp does have a search mechanism. The main differences are this:
In HTML Help you are working with a single compiled file. If your project has 200 topics, you still have a single file with a CHM file extension that has all 200 topics inside.
In WebHelp, it's uncompiled. So you have 200 individual topic files (and many other constituent files) that live in a file system. Typically on a server.