Amazon is continuing its push into online streaming video by letting its Prime customers purchase monthly subscriptions to HBO and Cinemax right from their Amazon accounts.

HBO will be available on Prime for $15 a month, while the Cinemax add-on will cost $10 a month, Amazon said in a release. You can already access some HBO content on Amazon, but by selling subscriptions, the company is taking things to a new level.

Both channels were also recently announced as add-ons to AT&T's new streaming service, DirecTV Now, highlighting HBO and Cinemax's attempts to reach beyond their traditional audience of cable subscribers. As many as 20 million U.S. households lack cable TV, AT&T estimates, either because they canceled their plans or because they never had one to begin with.

While it may seem odd for Amazon to offer yet another way to get HBO when consumers can already get it directly through HBO's own streaming app, HBO Now, for exactly the same price, being able to consolidate your bills a little could be useful. For Amazon, the premium channel serves as another incentive for Americans to sign onto Prime, the company's lucrative membership service. (Amazon founder Jeffrey P. Bezos also owns The Washington Post.)

And because Amazon's HBO viewers will be watching "Westworld," "Game of Thrones" and other hit shows through the Amazon video portal known as Amazon Channels, the company may get credit for all that streaming when analysts compare it to the likes of Netflix and Hulu. Numbers from Sandvine show Amazon Video accounts for 4.26 percent of all Internet traffic consumed in North America during peak hours, versus 35 percent for Netflix.

If more people start streaming "Silicon Valley" and "The Night Of" through Amazon, those numbers could rise. And that would be good for Amazon.