Most likely culprits are lower light levels--almost inevitable in the house--and lower humidity. Your brightest sunniest window in the house is about the equivalent, or so I've been told, of full shade outdoors. With these great new CFL bulbs you could boost the light to them fairly easily, I think. Some people use humidifiers for their houseplants to increase humidity, but since I haven't done that I can't advise you as to the best ones. Some people swear by misting, but my understanding is that misting lasts about as long as it takes you to do it--in a dry house it doesn't last long at all. I've heard five minutes, but that may have been a joke or an attempt to illustrate the point. Anyway, I don't mist, but I do use supplemental lights. Don't believe I'd be very successful at all without them--my house is quite dark, except for all the plant lights!

It seems to be par for the course. All mine lose a few leaves and have some that turn yellow. I don't think there is anything you can do to reproduce the light outdoors inside unless you have a fantastic lighting system for them. I have found however that the ones in the boys bathroom do remarkably well, usually the light is on in there 24/7 (6 year old don't like to sleep in the dark) so I have been keeping the light in my bathroom and kitchen on all night, we shall see what happens with my little experiment (lol)

It is natural.
This is why before I bring plants in, be they houseplants or tender perennials coming in for the winter, I usually adjust them to lower light levels outdoors for about 2 weeks (the reverse of bring plants from in to out)before they come in. Doing this I get very little shock :D

Vera

I agree w/Vera..if you have the space to move your plants in a shadier outside spot, move out of the sun a little at a time, daily or every second day. Hopefully, doing so will prevent shock when plants are brought in our dark, stuffy, dry homes.
Yes, it's normal for leaves to drop..some plants take longer to acclimate.
Prepare areas plants will be winterized. Cleaning should be done before bringing in. Wash and wipe (walls, shelves and windows.
Keep temps as cool as possible. If possible, bring in before heat is turned on.
Decide which windows plants will winter in before bringing them indoors; choose the best area so a plant isn't costantly moved around, otherwise it'll cause confusiion and take much longer to adapt.
As soon as heat is turned on, turn on a humidifer. Make sure you have enough filters to last..
Hose off plants and pots before bringing indoors..unless you want spiders, earwigs, etc joining your family.
Though we all have our own ways winterizing plants, this is what I do. I not only hose outside, but take each plant to the sink and rehose. I use organic, home-made insecticides and Fish Emulsion. FE prevents scale and works as a last foliar feeding.
If you have your own insecticide methods, use after foliage is dry.
Set sun loving plants in south or west windows. Medium light lovers in medium light, and low light plants in medium light exposure..North or east.

I believe preperation is mandatory..finish cleaning and deciding before plants come in..They'll only be in the way while working. If you plan on setting up lights, check to see if they're working..Like humidifer filters, make sure you have working bulbs and filters so you don't have to run out the last minute. Also, clean bulbs so dust doesn't prevent blockage.
I'm a firm believer is misting. When plants first come in, I add a few drops of dish soap, citrus rind, and garlic in water that's been sitting out overnight. Shake bottle thoroughly. Then mist away...Good luck Toni