Well it does depend on your type of grass, the soil the local weather conditions etc.
A quarter inch is desirable in my book. It denotes a normal healthy lawn in my area. No "thatch" is not normal and it leaves the soil uncovered so it dries out faster and is subject to causing wide swings of soil temperature, which is not good.
De-thatching is over sold in my opinion. In most areas a healthy lawn will not need it. Over fertilizing can cause to much of a build up in some areas.
1/4" of thatch is perfectly normal and not a problem. Thatch only becomes a problem when it becomes so thick and dense that water can't penetrate. That's probably around an inch or so. Most people mistake the normal decaying matter on the soil surface as thatch, which it really isn't. Sounds like that is what you have here. Google a bit and you can find pictures of real thatch. When you take a 6" square piece of turf up, it looks like a thick, dense layer, almost like a thatch hut roof. It's generated in varying amounts by different types of grass and as the previous poster pointed out, excessive fertilization will increase it.
If you want to aerate, you can do it. I would not do it based on the observation of 1/4 of thatch. If you want to do it to reduce compaction, overseed, etc, that that could be appropriate. And I would definitely not de-thatch, because you don't appear to have a thatch problem and de-thatching is more destructive in the sense that it rips apart and kills a lot of good grass in the process.
Unless your lawn is compacted, aeration is not really necessary. Removing 1/4" thatch is not needed, unless you plan to overseed shortly thereafter. Use less the recommended lawn fertilizer salts and consider applying an organic fertilizer (composted manure, seaweed, pellitized chicken manure, Milorganite, etc) once a year to encourage earthworm activity which will aerate your lawn.
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