IIS doesn't allow SSL access on multiple domains on the same IP address. Only one domain on IP address can have SSL support. It is SSL design. As you know, certificate is signed for certain domain. Domain exists on one IP address. SSL protocol handshake is to connect on certain IP and request its certificate. Certificate contains domain name for which it was signed. If browser asked same domain, it doesn't show warnings and work using the certificate.
Apache (at least Unix version) allows to use certificate for some domains on one IP address.
IIS doesn't allow it. Plesk for Windows team tried to allow SSL support for multiple domains on a IP address. Special ISAPI filter was created. This filter causes some problems with FrontPage and new version was decided to develop without extension. Also some other ISAPI extensions were removed. I think a lot of people heared about Server.MapPath and #include directive problems. It was a problem caused by ISAPI filters because some functionality was added to IIS but IIS does not support it. Main idea was that Plesk for Windows should had same functionality to Unix version. Some functionality was created the same without problems, other caused serious issues. So some functionality was created incompatible with Unix version in Plesk 7.0 for windows. I don't think it is bad because main functionality works Windows native way.