Yes, absolutely normal. Cheapest fares to Europe generally require roundtrip purchase (check pricing on one-way's and they are also very high) along with a Saturday night stay. Also, the cheaper fares will typically have advance purchase requirements (28 days is fairly typical for the cheaper O fares to Europe). The fare requirements on these cheaper fares are all detailed in the fare rules (which you can find on aa.com prior to checkout or on third party sites like ITA Matrix).
It's a form of fare discrimination between business flyers and leisure flyers. Business flyers often do not want to stay over a weekend because they would rather be home and are less price sensitive than leisure flyers. They also tend to buy their tickets closer-in than leisure flyers. This type of fare discrimination used to also be quite common on domestic fares, but Southwest has squashed it on many routes as their cheap fares do not have any kind of roundtrip or minimum stay requirements (they are all priced as one-way's) and the legacies tend to match Southwest fares and fare rules on routes where they compete. You can still find these fares on legacy airlines on routes where they don't compete with Southwest.
Because you are based in Dallas (where Southwest has a large presence), you won't often run into them unless you fly AA into smaller markets that Southwest does not serve. As a counterpoint, Delta still has many such fares on domestic routes out of DTW because Southwest has a fairly small presence there. The pricing difference between roundtrip and one-way fares on domestic routes is not as extreme as international, but the different fares do in fact still exist on legacy domestic routes.
Last edited by xliioper; Jul 18, 2019 at 9:10 am