I seriously doubt a developer would slow down work on a project because of a bad economy. First of all, developers enter into a contract with the construction company to finish the building by a certain deadline or else the construction company pays fines for being behind schedule. I've heard some deadline fines can be up to $70,000 a day. The construction company that built the Grand Hyatt in San Antonio learned this the hard way. Also most of the construction equipment on the job site is rented. Most tower cranes can cost thousands of dollars a day to rent. So if a construction project sits idle, they'll still have to pay for the crane rental and other equipment. I would expect a project to continue on schedule and even at a faster pace if times were hard. The time that I would worry about a project is if equipment started to disappear from the site such as smaller equipment like trucks and forklifts.
As for the current projects, they all seem to be on schedule and moving at a regular pace. We've had a dry year this year, so there's been few rain delays. The Four Seasons seems to be doing fine as is the W. Below grade construction is always tricky, so as the W moves above street level I would expect it to shoot up fast. As for the Ashton, it makes no sense at all not to put windows on the building and make it weather proof. Who wants mold in their unit? That would only add to the cost of the project if mold took over and had to be cleaned up before the building could be finished and occupied.
Of course, stuff does happen. Just ask the Chicago forumers:
http://forum.skyscraperpage.com/showthread.php?t=119993&page=125