When you think it through completely, you'll see there's good reason for the dupe detector to be lenient. In the early days of HN (or earlier, as "Startup News"), avoiding dupes was more important since the rate of submissions to the /newest queue was fairly slow. These days, the rate of submissions is very brisk, so a lot of really great stuff floats by basically unnoticed. Allowing for a second chance actually makes sense.

If you have "Show Dead" on, you'll see there are a lot of people submitting who have their submissions immediately marked [dead]. If you've studied how HN is built, you'll see pg (et al) tends to follow an "Enough Rope" design policy -- this is from the old expression "Give him enough rope to hang himself, and he will." It seems if you intentionally and repeatedly abuse the lenient dupe detector to promote something, you will be noticed, silently, and handled accordingly.