Serial Peripheral Interface
A few points. That Maxim article targets a specific type of spi device. Mainly ones that are write only. Notice only MOSI is shown, not MISO. Additionally, these devices are chained, so data is shifted from one device to the other, like a shift register. (One common use of SPI peripherals on a microcontroller is to use them to drive common shift registers.)

SPI does not require the master to receive data. A slave is not required to respond. You can even have read only SPI devices, where the Master just clocks in data from the Slave (Only uses MISO). You can even have a 3 wire variation where MOSI and MISO are tied together (half duplex only). It all depends on the type of spi device you are using. Additionally, SPI can do Full Duplex transfers, but not all devices support this. As Wikipedia states, most devices do half duplex, even when wired in 4-wire mode.

In that note, the SPI devices are write only.

As for the clock frequency question, there is no auto negotiation of clock speeds. This is decided while the master is being programmed. You have to account for it.