You're comparing the average salary of all H-1B jobs (developer, accountant, analyst, etc.) to the salary of a developer. Instead, look at the average salaries for H-1B software engineers in 2016:
Facebook @ Menlo Park: $152k
Google @ Mountain View: $130k
Apple @ Cupertino: $154k
Amazon @ Seattle: $124k
Microsoft @ Redmond: $120
So comparing base salary alone, these companies are definitely not underpaying their H-1B hires.
To see salaries for yourself, you can go here and filter by year to see the latest data:
Facebook @ Menlo Park: $152k
Google @ Mountain View: $130k
Apple @ Cupertino: $154k
Amazon @ Seattle: $124k
Microsoft @ Redmond: $120
So comparing base salary alone, these companies are definitely not underpaying their H-1B hires.
To see salaries for yourself, you can go here and filter by year to see the latest data:
http://h1bpay.com/companies/Facebook/cities/Menlo%20Park-CA/...