Tharen the Damned said:
What is the difference between Demonprince/Archfiend status and godhood for you?
Gods are tied to their worshipers, while archfiends (and archcelestials, archmodrons, etc.) are tied to their planes of existence. Archfiends thus work on a bigger scale, in most cases, representing infinite swathes of real estate where gods represent finite groups of the faithful. This doesn't mean archfiends are more powerful, but they're certainly vaster - to some degree, they and the planar layers under their control are one. A divine realm, which has a similar connection to its owner, is a more finite thing, although it may seem endless from within. Divine realms also have no real connection to the plane on which they're hosted.
Deities don't truly personify their alignments as archfiends do. Cyric, Nerull, Incabulos, and Tiamat are all evil, but the General of Gehenna is Evil Itself. Hextor is lawful evil, but Asmodeus is Malign Order Incarnate. If Asmodeus were to die, his associated alignment would be shaken, fragmented; lawful evil items and races everywhere thrown into confusion and disarray until a new being stepped into Asmodeus' place.
A being can certainly be both; Lolth is both god and archdemon, for example, as is (I remain convinced) Baphomet, Demogorgon, Yeenoghu, Kostchtchie, and Sess'inek due to their substantial worshiper bases. Graz'zt, Pale Night, Lynkhab, Fraz-Urb'luu, Alzrius, and so on are only archdemons, and Orcus lost his divinity during the course of his resurrection.
Graz'zt, at least, seems to actively avoid divinity, seeing gods as pawns for him to manipulate, not beings of equal merit to respect, and certainly not something for him to strive to become. When he had Waukeen under his power, he asked her not to grant her divinity to him but to his daughter. Rather than insist the xvarts worship him, he permitted his servant Raxivort to become a lesser god under the power of their prayers (Raxivort nearly wrested control of Azzagrat from him, which would have made him an Abyssal lord as well as a god, but Graz'zt managed to hold onto his throne despite Raxivort's power). His son Iuz, a demigod, is also something he seeks to control and direct; when Iuz became a demigod through the power of the Soul Husks and the worship of his followers, Graz'zt didn't seem concerned with doing the same.
Archfiends might well be limited in some respects to vulnerable bodies, although in 1e they had "demon amulets" that protected their essences in the same way as lich phylacteries. In
Dead Gods the PCs have a chance to find Orcus' amulet, but it's noted that now that he's a god (as he was at the time, albeit an undead one) it has no power over him. Being a god was also what gave Orcus the chance of coming back at all; if he had remained a "mere" archfiend, the Abyss would have simply swallowed him up when Kiaransalee slew him on his home plane. This is likely why beings like Orcus and Demogorgon bothered with divinity, Orcus seeking cultists among the necromancers of Trask and Narfell and Inuitea (from the Ghostwalk campaign) to become a deity, big and flashy and obvious. Demogorgon sowed his seeds among the ixitxachitl and kopru and troglodytes, the mad dakons and Olmans and ur-Flan, and became a lesser deity as well. Graz'zt has his cultists among witches and lamias, but he prefers a subtler path. He redirects divinity when he finds it, remaining hidden in the shadows between. Even so, he manages to have as big a power base as his divine rivals. He's not the only archfiend to feel this way, either - yugoloths find divinity abhorrent as a rule, and I don't see beings like Pale Night or Rhyxali bothering with it any time soon. I'm convinced that this is because godhood, for a being who already personifies part of the cosmos, is as much a burden as an asset.