As those scripts are entirely CGIs, they are slower as they never maintain persistent data in memory but store it and load or parse it each time the search engine is invoked. Working as a permanently running server and answering to multiple search requests simultaneously this category of search engines requires more hardware power, more memory and is aimed to larger sites that really need a good search engine. Alkaline is designed as a server persistent search engine. Technically, search servers maintain indexes in RAM or use some internal swap mechanism. They have complex algorithms for searching and indexing, usually jealously kept secret by their designers.
Cells are fast and resistant to growing data.
Of course, there's no mystery that a big server with a lot of hardware power will search faster and will be able to index a larger site. Existing Alkaline powered sites maintain an index of 500'000 pages with about 450'000 word forms and run on industry average Pentium III or Sun Ultra servers. Such a configuration can handle from two to three search requests per second. Finally, Distributed Servers target searching and indexing of the whole web. This is the most fierce long term fight of search engines as large companies compete for the best technology and for the most relevant search results.