The median household income has recently been just above $50k for the US (since around 2006), so I think the requirement is probably based on wanting shoppers from the upper half of that statistic.
A quick googling brought up a list of medium incomes for various Los Angeles communities. Not so surprising that the hardest ones to schedule shops for are amongst the top ten are listed here:
1 Bel-Air $207,938
2 Hidden Hills $203,199
3 Rolling Hills $184,777
4 Beverly Crest $169,282
5 Pacific Palisades $168,008
6 Palos Verdes Estates $167,344
7 San Marino $158,855
8 La Cañada Flintridge $148,996
9 Rolling Hills Estates $145,628
10 Malibu $138,215
In one of the more surprising stats, Bev Hills falls pretty far outside this top 10
37 Beverly Hills $96,312
..and one of the most embarrassing parts is that my neighborhood was dead last:
265 Downtown $15,003
Interesting that one of the very steakhouses that spurred this discussion is located within walking distance of me, however.