That's part of it. The other part is "write using tools which lots of developers are familiar with", i.e. the general browser stack. That still applies.

For that matter, even if your app requires occasional core high-performance bits written into C, that's probably still a benefit to you. Similar to the standard Python argument, which advocates a very similar development pattern.

After all, it's not like you're not compiling it on each platform anyway to get the native app you're distributing.