The point is that Java webapps are multihreaded. Classic Ruby apps require dedicated process for every parallel request. Hence your 4GB java app may still be more efficient than 500MB Mongrels.
4 gigs for a search index is rather meaningless. It's based on the size and number of documents you need to index, and not so much on your language or tool of choice.
Correct. But the lucene index requirement was bounded by the fixed size of a CMS. There were ~5k products and they were aggregating consumer reviews from various sites. The 4GB was not an strict limit, but it was what we needed to store all the user reviews of all the products, allowing for up to 20 reviews per product.
