Well I guess the device wouldn't know the correct web server, which was kind of the point of my question. ISA 2006 allows me to publish multiple servers using the same port and then redirect as appropriate, for example:

External FQDN of mail.example.com on 443 => Internal FQDN of serverA.domain.com on 443

External FQDN of web.example.com on 443 => Internal FQDN of serverB.domain.com on 443

and so on...

My question was can I replicate this behaviour with the 4400N device and like I said, I think the answer is no. If that's the case then I'll likely just stick a Unified Access Gateway box behind the 4400N and use it to publish my various servers, though I'd prefer not to.

No. You cannot do that with the WRVS4400N. You can only forward port 443 on your public IP address exactly once, i.e. to a single LAN IP address. The router does not know which FQDN you have used to access port 443 on the public IP address. That's a general problem of HTTPS as it wraps HTTP inside of an encrypted SSL tunnel. The host name accessed is part of HTTP, i.e. it's inside the SSL tunnel. If the router had to redirect the traffic to different servers it would have to operate as SSL endpoint to learn the host name information of HTTP. The router does not support this.