How many active retail brokerages are indeed in existence today?

[Toibit]

It must be in the low thousands.
As the gentleman above pointed out there's over 1200+ registered brokers using MT4 terminals.
Astounding when you think about it

The issue on counting the number of brokers on the MT4 server is that many brokers have multiple trading server hence you might end up to count one broker multiple times. I don't think there are more than 200 serious brokers who actively offer their services and don't scam people.