1) This data came from TheKnot.com, a website dedicated to wedding planning. The web site makes money via wedding vendor adverting. Survey participants were TheKnot users. So, the survey participants 1) have internet access and 2) time/inclination to spend online looking at wedding ideas and 3) enjoy posting to wedding message boards. Hardly a representative sample, despite the large n-size.
A bit of evidence for a non-representative sample comes from basic demographic data available for the survey. The survey press release states that the average age of bride was 29 and the groom was 31. Census data states that the US, the average age for a bride is 26.6 and the groom is 28.6, indicating that this sample may be coming from more established adults (with deeper pockets).
2) According to the methodology for this survey, this data is based upon individuals who paid a professional for the services provided. If you had a friend provide a service for free (for example, my Aunt, a minister, kindly officiated our wedding for free and friends who are musicians provided music for the service), your data point of $0 would not be included in this data. Likewise, if you didn't hire a limo or a videographer, your data point of $0 would not be included in this data.
3) As a social psychologist, I would also use this as an example of a merchant attempting to establish some very expensive social norms for people planning weddings.
Finally, if you go to the original data linked above, they do detail how wedding costs typically reflect the cost of living for a region (so, perhaps regional data would better reflect on a true average, another discussion point for your students).