Scala's type inference makes the typing a lot less of burden, when compared to java, but it is still there.
Just our options. Feel free to make your own. People with lots of Groovy experience may choose Groovy, and those who really don't need much metaprogramming support may choose Scala. This is just not our case.
Some people also feel very uncomfortable with the lack of almost perfect auto-complete. Ctrl+k (text complete) on Netbeans is magical enough for us most of the time. We use lots of TDD, such that we can also refactor safely, therefore, type safety feels more like a burden when writing tests for things that don't exist on statically typed languages than on dynamic. Again, is a matter of taste as well.
For example Grails and groovy were supposed to be big on the java framework but due to seveeral reasons they seem to be really more niche. PArtly because it seems the people behind both of them just arent dealing wiht the problems such as bugs quickly enough.
Scala is an interesting language but again there doesnt seem to be a heavy push for it. Expect for peopel that are using it and know what its strengths are.
All of which leads to alot of confusion about which technology to use.
Then theres the issue of frameworks. Theres a million of them but none of them really stand out. ANd personally i dont think it helps that oracle is no running things.
On the other hand ruby is known by many people as being pretty powerful and used by alot of startups. Same thing with php. How many startups do you know that use java? I know foursqaure uses liftweb but thats about it.
Flightcaster, which is funded by YCombinator, uses clojure and Ruby on heroku (more on their infoq profile: http://www.infoq.com/articles/flightcaster-clojure-rails).
Most startups are not actually vocal about what they use. Most of them actually are not heard, so they could be as vocal as they wanted and still noone would hear them.