I've noticed this seems to happen to everyone. The little things are eventually done away with, if not completely, at least for the most part. Sure, we still pay for each other's dinner quite often. If she's got a sore back, I'll massage it. Not that it's necessarily a bad thing to lose most of the little things. It might be more practical to not waste 3 hours preparing a home cooked meal, and just pick up some fast food instead. Going out to fancy restaurants all the time can drain the wallets, and put a financial strain on the relationship (as can buying little gifts all the time).
Maybe at the beginning of a relationship we feel a need to secure things into place. Making sure she knows that you love her by holding the door open for her, buying her dinner, and then giving her a little present. Then you got dinner and a present and want to give back to the relationship, so she gets a back massage and a present. And then you both end up feeling securely in place, as if by romantic hot glue, and you don't try so hard. You both know you love each other without the need for all these little favors.
You don't need the little things to tell you that you're loved, but it helps. If you've been together for 2 weeks or 20 years, you should still try to keep a few little things alive in your relationship. Special occasion? Take her out for dinner. Did she have a hard day at work? Maybe a back rub and some candles would be nice. Not her birthday but you just want to let her know that you still love her? By all means, buy her a present!
The little things may gradually disappear over time, but they don't have to disappear altogether. So buy her a candle tonight. Maybe she'll make you smile and break out the peppermint lotion.