I'm not sure it has anything to do with not hearing words as it does with not having to use any words. They don't HAVE to talk, they don't have as many different situations in which to be forced to use them, and they don't have the repetition/participatory situations as they do in daycare or preschool where they have circle time or have music playing that they sing along with. Kids at home often have their needs anticipated by parents, and 2nd kids often have their needs anticipated better because parents are doing it with more experience and read their body language better. Be sure to put a variety of sounds in front of her - play CDs with music & words, do DVDs with finger plays or action sequences along with music, etc. A child will learn "animal sounds" faster by singing "Old McDonald had a farm" more quickly than with someone asking "What does the cow say?" - it's more fun, it's repetitive, it's musical and it helps them form sounds in a rhythm. Also read more, particularly books that encourage participation by the child. With familiar books, let the child finish the sentence for you, even if you ask, "How does the next part go?" or something like that.
I think the "it's because you are home with her" is a subtle jab at SAHMs - or maybe not-so-subtle. Not necessarily by the person who said it - they may have internalized it from other sources. For years, no one went to day care and we all learned to talk! So I think it's a bad think when working parents are pitted against stay-at-home parents.
Kids develop individually, and if they aren't working on their talking, they are developing in some other area. Your 2nd child may have motor skills (fine, gross) or other developmental advances ahead of your first one -- the talking is just what people notice. It's great that you are not worried about it! Mine didn't talk at all until 16 months, but he was ridiculously advanced in walking, running and many other areas. So, as you say, she will catch up!