No, the RAM is a separate chip. On the BCM2835 devices they use a package-on-package arrangement so on casual inspection they look like the same chip. On the Pi 2 and Pi 3 the RAM is on the bottom of the board.
There is apparently an architectural limit in the Videocore 4 that limits it to 1Gbyte.
Yeah, I keep thinking about how a tiny device with oodles of RAM would be such a killer Redis or static asset server. Or even a killer database server, for read-heavy loads.
Although am not even sure if that would be possible in the near future - for SoC's like the BCM2837, the RAM is on the same chip as the CPU+GPU, right? I don't even know if it would be feasible to build gobs of RAM into a package like that.
Of course, RPi's are still freaking awesome, and I am happy they exist.