In the e-commerce world, the difference between 2ms and 200ms isn't that big of a deal. Search relevance, however, might be something that is important. It looks like that is something they are focusing on heavily.
In term of relevance, we have developed a ranking algorithm specialized on that case that provide better results than traditional approach: http://blog.algolia.com/search-ranking-algorithm-unveiled/
SQL queries are not relevant for text query, for example you have no notion of tokenization or proximity between words.
We plan to write a blog post on limit of SQL based search.