There is still more developers would love to cram in but there is about 0.5/2s window where you can load before people get bored and leave we just load more crap and do more client side processing now to use up the bandwidth and CPU.
Contrary to the popular belief on slashdot us professional web developers do not sit around thinking of ways to use new browser features to make sites as slow as shit.
Instead clients come to us as some graphic designer has mocked up this amazing new site for them with tons of flash animations they created, psd files that represent all aspects of the site with each layer representing a different page and some notes on which bits of the site need to be easily editable by the client, which bits obtain dynamic data from another site (like the companies aher price) and finally, with a detailed list of which tracking they want to use to track users journey through their website.
Yup. much of this tracking crap is actually added at the clients request because they want to track how their users browse the site and what advert they clicked on a different site which brings though the clients who buy and what adverts on other sites just generate them click throughs but none that result in a purchase or sign up or whatever they want from the site.
Web developers have to work through this crap and try and convince the designer that some of his design elements are going to kill the page loading time and are uttterly pointless. The ones that have to stay they try their best to make efficient by re-implementing it completely in JQuery or whatever. Try and convert the pointless flash object into a much smaller animated GIF or PNG since it is has no interactivity and is only flash as that is what the designer has tools to create.
They then finally try and steer the client to only implementing the tracking shit on the pages that that are REALLY important (index, basket, purchase complete, etc). But no, the client first insists on the third party tracking be used to track every goddamn product so they can have all the analytics in the system their marketing chumps like using and not forcing them to login in to your site as well. Then they decide that the site is too complicated or something so you need to add the tracking to every page in the help section, then they notice that loads of people get to the index but never buy anything so you have add tracking to find out why (they load the index and decide it loads too slowly then fuck off to a quicker site probably due to the analytics shit).
Finally, the client realises that when the get stuff demoed to them it was done in a designers office with fibre to the back of the demo PC, tests their web site at home and realises everything is slow as shit and asks you to find out why. You tell them, and they say that blaming Google or whoever does the tracking is just passing the buck as the google home page loads really quickly, you must have messed up in creating their site instead.
At this point the web developer realises he can't win and shoots himself in the head :)