It's not a question of having JavaScript enabled/disabled. It's a question of whether the JavaScript gets delivered from your server to the client's browser properly and fully in a state that it can be executed successfully. Progressive enhancement is about robustness, being adaptable when the network fails to be perfect.
Look at it this way, this __escaped_fragment__ is only supported by Google. No other search engine supports it. And considering that building it with progressive enhancement first, and then enhancing it with JavaScript, you get content that's indexable by any search engine, not just Google.
The workload is the same, the complexity is the same, the only difference is the focus on progressive enhancement first rather than try to bolt a clearly less optimal solution later.
Look at it this way, this __escaped_fragment__ is only supported by Google. No other search engine supports it. And considering that building it with progressive enhancement first, and then enhancing it with JavaScript, you get content that's indexable by any search engine, not just Google.
The workload is the same, the complexity is the same, the only difference is the focus on progressive enhancement first rather than try to bolt a clearly less optimal solution later.