Yeah, I remember that back when W first started there were some concerns that there was a curse on Kamen Rider actresses. Miyuki Kanbe from Hibiki died (:(), Yui Satonaka from Kabuto got really sick, and Yuriko Shiratori left Den-O for fairly vague health reasons. There were some concerns around Hikaru Yamamato when W started after rumors started surfacing that she'd posted explicit pictures of herself online and/or had plastic surgery. For awhile there was speculation that she'd be kicked off the show.

So...is that why Hana stayed a little girl even in the movie?

Yeah. From what I've gathered there was some initial uncertainty about whether or not Shiratori would be coming back to the show. Ultimately she didn't, which led to Kohana being a permanent part of Den-O (until she disappeared, too, at least - I vaguely remember reading that the actress retired to focus on school).

Thats what Id heard as well. Its unfortunate that Yuriko had to leave the show but Kohanas actress did a fine job as well. The only real problem with Yuriko, and for that matter Takeru Sato, leaving the franchise is that they were singularity points. They weren't supposed to be change by time shenanigans. But thats the only reason ever given as to why they changed :(

You have to cut Takeru a break. He played Ryutaro for the full series and 3 movies, and not everyone is gonna be like Renn Kiriyama, huge KR fans willing to come back year after year.

They could've saved them alot of trouble with very little work. Just do the series starting with Momo has Den-O. New Imagin, new Rider to help. So instead of varied forms you have many Riders.

Screw that.
I hate Momo as Den-O. Ryotaro was the best.

That would be too brave of an idea. Having a show with a monster as the main character isn't something Toei knew would work; I'm pretty sure the popularity of the Imagin wasn't something Toei anticipated.

At the moment I'm watching the Kamen Rider Decade musical/stage show from KITSubs.

Singing Riders are unusually entertaining.

Diend's song is the best :lol