You are right about the idea of 'shrinking the possible variants'. In fact, the possibilities are not only reduced - they are LIMITED to just these two. That is the function of the definite article: it restricts. The use of the definite article tells us that the writer uses ONLY these two programs and no others. We use 'the' to refer to particular, specified nouns and to exclude all others.
For example, if someone says "Those are programs which I use", we know that they use many different programs and these are just two of them. Likewise, if they say "That's a program which I use", we know that this is only one of several programs which they use. The use of the indefinite article (singular) and the zero article (plural) indicates the existence of other things in this category.
However, if someone says "Those are the programs which I use", we know that they use only those two programs. Likewise, "That is the program which I use", we know that it's the one and only program which they use. The definite article excludes the existence of other things in this category.
I hope that this explanation makes sense.