If you can't imagine writing a spelling corrector from scratch you might want to take a minute and broaden your horizons(I know it was magic pixie dust for me before I read it). http://norvig.com/spell-correct.html
Stemming could be accomplished just as easily, put in a word get back a list of stems. Just a dictionary look up that could be precomputed.
I thought his comment was more along the lines of "I cannot imagine writing industrial-strength versions of all of these things Lucene gives me."
Yes, you can write a spellchecker in 21 lines of code, that doesn't necessarily mean it will be fast enough to be a component in website search or that it will be any kind of a pleasure to query or maintain the word corpus.
I can put together toy versions of many things Lucene provides pretty easily in my own time. Building useful, dependable versions of most anything takes a nontrivial amount of time and effort, so it's smart to restrict my usage of toys to understanding the concepts.
Stemming could be accomplished just as easily, put in a word get back a list of stems. Just a dictionary look up that could be precomputed.