Yes, we experienced the same mismatch, too. I had the same worry. Our read-alouds had progressed to the 5th-6th grade reading level before she started to read first grade level books. I remember at one point I had intended to get out all the simple board books I had packed away. I never got around to it. She learned to read using books like "Frog and Toad" and is now reading her way through the "Henry and Mudge", "Poppleton", and "Mercy Watson" series.
Perhaps, had we stuck to age-apropriate books she would have learned to read those earlier. But, would she have progressed through the next few levels as fast as she did? I don't think so.
FWIW I have yet to see her have trouble comprehending anything she is able to decode. And, I actually think her comprehension boosts her decoding skills. So, I totally recommend reading more developed books to your young children. My DH continues to read a few chapters to DD each night because of the wide berth of benefits.
Now, writing is another story. She will be reading fluently before she can print more than her name.
