common emitter configuration of BJT
erece & uart,
I believe I offered an explanation of why the Ic current lines are horizontal in a CB configuration and have a slope in the CE configuration. See post #3 of this thread. The Early effect effectively puts a shunt resistor across the collector current generator and reduces the transistor's performance. The slope of Ic shows the resistance of the collector circuit. I said that the more vertical slope of the CE configuration was because the transistor see its output resistance as rc/(β+1), which is smaller than the CB impedance of just rc. The lower resistance is why the lines show a more vertical slope. Any good book on transistor circuits will show that CE and CB have a different output impedance.
I don't think that the smaller value of α compared to β makes any difference. They both have a one to one correspondance to each other. The output resistance of CE can be expressed as also as rc*(1-α), which is identical to the value above.