Not so.
iWeb has actually been around since the first edition came out in 2006 and it started with iWeb 06, then iWeb 08 and finally iWeb 09.
It was primarily designed to go with dot Mac and then MobileMe, which were accounts that enabled you to publish websites. Unfortunately, after this things seemed to be cloud based, which is why Apple developed iCloud, but they decided not to offer web hosting, hence why both dot Mac and MobileMe disappeared and there was then no need for iWeb because iCloud does not offer web hosting and there are lots of companies out there that do offer this and as Apple are primarily a company that sells products - computers and phones etc., they decided to leave the software to other than know better, which is why it became unsupported and they do not sell it any longer and why iWeb has not been updated for the last six years.
It is time to move onto other products which are better and up-to-date. There are lots out there and Rage Software has developed EverWeb. Take a look. It is very like iWeb in look and feel and you can do lots more things from inside the application, that you could not do in iWeb.
As far as Flip For Mac goes, you may just have to wait a while whilst Flip catches up with the new OS and it will become compatible eventually. Things just need time to catch up.
You have come to Macs late, so it is time to move on from iWeb and use other software that is supported and will work. There is plenty of it out there and you just have to look around and take a look at EverWeb - I have provided a link for you.