I think that what you are calling web slideshows are now called "web galleries". That's a way to store and organize your pictures with a 'filmstrip' to navigate easily in your photo collection. That's something like the F11 full view to run instant slideshows on your computer. You can store such galleries in your own personal website or export it to be used on a different computer.
Unfortunately, you are right that the feature has been removed from Photoshop Elements in PSE11, together with the ability to create your own customized slideshows with transitions and effects. The main reason was the necessity to offer a 64-bits version of the plugin; but there was also another reason for the web gallery. It relied on an old Adobe platform which did no longer offer security against web attacks.
So, now you only get automated, not customizable slideshows with PSE, you need Premiere Elements for that. Web galleries are available in Lightroom.