Physics discussion warning! Skip to the end of my first response for the easy answer.
That advice is perfectly good and is a separate consideration from interference with reflected waves, dealing with conditions for amplifying standing waves - frequencies which the room makes things much louder. These frequencies are usually called "room modes".
In short, having the source of your sound - the speaker driver - at the edge of the space makes it easier to create standing waves. You can also amplify room modes by having the driver half way between walls, a third of the way, a quarter, etc. The best placement of the driver is usually a different prime fraction of the distance between surfaces, e.g. 3/7 along the width, 2/5 along the length and 2/7 between the floor and ceiling. Good luck making that work for multiple drivers.
This is a rare example of a simple calculation you can do based on the relationship between the speed of sound, the distance(s) between walls and the frequency. Standing waves can occur at half, whole, double, triple, etc. wavelengths with the significance usually decreasing with each multiple. Conditions for quarter wavelengths are more complicated (involving openings).
For example my long and narrow home theater is 4 m wide. The speed of sound is about 343 m/s. 343 m/s divided by 4 m is about 86 /s, i.e. 86 Hz. This means that I can have standing waves around 43 Hz, 86 Hz, 172 Hz, etc. You can do similar calculations for length and height.
What you find is that for almost all listening spaces, these frequencies are bass which are very near of beyond the lowest end of most speakers and are within the range of subwoofers, hence the complications with and advantages of proper subwoofer location.
Your receiver's auto-tuning or your manual calibration will often substantially take care of room modes above the subwoofer crossover (e.g. 80 Hz for THX), but correction for sub-bass frequencies is usually a tricky manual task (discussed in detail in other forums).
In conclusion, don't worry about your speakers being somewhat close to the wall, but do position any subwoofer carefully.
By the way, does anyone have any idea which of the following would make the best setup when paired with a sub in a small room, and that would be used mainly for movies and games?
1. 4 FS52s
2. 4 BS22s
3. 2 FS52s + 2 BS22s
Remember that it's 4 (or 2) BS52s + 4 (or 2) speaker stands when considering cost and that a floorstanding speaker is effectively a bookshelf speaker with an excellent stand and better sound. Therefore you should use floorstanding speakers wherever possible and affordable.
BTW, I note and approve of the lack of center speaker. While my bedroom theater includes the enormous SP-C21, my home and office theaters both have a phantom center. This works really well and is most convenient when the speakers and space are properly calibrated.