>without an individual subscriber receiving too many deals.
Correct. 1 refers to the rate per individual inbox that was entirely essential for their initial growth and traction. Total volume and market segmentation > 1 ... is a no brainer for any business. While they can now afford to alienate and loose businessmen and others with low inbox noise tolerance, limiting the bandwidth they consume in each individual's inbox is still their weakest link and one of the only ways for them to actually loose subscribers.
Urban sprawl has connected the city where I spend my day with the place where I spend the evening. I"m not the only one either as many make the short commute. It would be nice to get an email from Groupon with both daily deals in a single email, if I choose.
Targeted deals based on real-time inputs (weather, slow day in the business, new story about a competitor, etc).
Add in hyper-local targeting and enough automation and you have the holy grail of local commerce.