"I Melt With You" has been in a lot of commercials over the years. The two that come to mind are Hershey's chocolate and Taco Bell.
As for oldies76's discounting the song because it did not make the KROQ year-end chart, there are a couple of good reasons for that. (And bear in mind, I am something of an expert as to what constitutes a 1980s New Wave hit, since that is the music programmed on my consulted format The Eighties Channel.)
First, the song got prominence in the movie "Valley Girl", and even though that wasn't enough to get it listener votes for the year-end KROQ list (movie came out the same year) repeated plays of the movie on television made it more familiar to the audience -- plus all those commercials -- and it therefore eventually made it to both the Flashback 500 and the All-Time Request 500, both of which are more important, research-wise, than the year-end charts.
Second, the band stayed active past the 1980s, touring with other New Wave/Modern Rock acts like the Fixx, and so the song continued to be performed in concert. While concertgoers are, admittedly, a relatively small percentage of music fans, it kept the song more in the forefront than it would have been if Modern English had simply disbanded and never performed it again.
Third, when VH1 Classic came onto cable/satellite, it was entirely a video music channel (and, like every other music channel Viacom has ever started, eventually morphed into a channel of MTV "original programming" reruns ... but I digress) and about 25% of its day was 1980s videos. About 75% of the videos in those hours were 1980s New Wave, and "I Melt With You" usually played at least once every two or three days in those blocks.
Fourth (and this is the important part), "I Melt With You" has some very familiar song hooks in it. As David has explained, auditorium music testing consists of playing the recognizable hooks and the respondents rank it based on remembering the entire song from those hooks and how much they would want to hear the whole song on the radio on a regular basis. All of the exposure I listed above means that those familiar song hooks are embedded in people's minds, and that puts them in a good position to rate the song in testing. And, as David says, it must be testing well, or stations wouldn't still be playing it.
In fact, before the Sirius/XM merger, the latter twice did an all-time countdown on the "Fred" channel (classic New Wave/Alternative) and it ranked #21 among 2002 songs in the 2002 version and #108 out of 2044 songs in the 2003 version. You have to admit -- although I know you won't -- ranking in the top 5% both times, two decades after its original release, is the sign of a durable hit.
Explanation done.