its where the entire page is rendered. the memory is so the DS can process all the information being downloaded in a relatively quick manner. For example, a page with the memory expansion may take 20 seconds to show up.. while the same page without the memory expansion, if you could use the browser, would take 2-5 minutes. big difference
Currently there is no way of using the DS browser without the RAM cartridge, therefore no way of using the ROM from any slot-2 (GBA port) device, if you happen to have a slot-1 device (such as a DSLink or DS-X) AND own the original RAM cart it is possible to use the ROM.